The Last Adventure! is the 22nd episode of season 3, the Season 3-finale, and the 69th and final episode of DuckTales 2017. It is a 3-part series finale special  that aired on March 15, 2021 on Disney XD.
The future of adventuring hangs in the balance as the Duck Family uncovers earth-shattering secrets in a final standoff with the Fiendish Organization for World Larceny (F.O.W.L.).
Part One: A Tale of Three Webbys!
The family raids F.O.W.L. Headquarters, only to find mysterious clones that point to a larger F.O.W.L. plot against them.
Part Two: The Lost Library of Isabella Finch!
The family attempts a rescue mission, splitting up for a final confrontation with F.O.W.L. High Command. Meanwhile, Webby’s search for answers uncovers an earth-shattering secret.
Part Three: Tale's End!
It's the final standoff with F.O.W.L. as Bradford’s evil scheme is finally revealed, and the future of adventure hangs in the balance.
Part One: A Tale of Three Webbys!
At Funso's Fun Zone, the Duck family and various friends and associates are in the midst of celebrating Webby's birthday. In the course of things, Della learns from cousin Fethry that Donald is planning on going on a trip around the world with Daisy, news she finds difficult to take in. As the partiers gather for cake, they are observed by F.O.W.L., now joined by Don Karnage, who quickly realize that something is amiss. Sure enough, B.O.Y.D., Lena and Gosalyn take out F.O.W.L.'s cameras, and the group spring into action. Scrooge, Donald, Della, the nephews, Webby, Beakley Darkwing Duck, Launchpad, and Gizmoduck make their way into the ballpit, which conceals the entrance to F.O.W.L. headquarters.
Huey explains that Launchpad has been talking in his sleep, and has determined that the pilot somehow knows the complete layout of the secret base. Based on Huey's plan, Scrooge and the kids go to find the "Missing Mysteries of Isabella Finch" while Donald, Della, Launchpad, Gizmoduck, and Darkwing set out to capture F.O.W.L. However, the two teams soon determine that the base is virtually empty of personnel, with the Missing Mysteries nowhere to be found. Startlingly, they come across two young Duck girls in a pair of tubes. Upon returning with them to McDuck Manor, they are able to verify that the pair, who introduce themselves as May and June, are in fact clones of Webby.
Beakley forbids the kids to interact with the clones, but Webby is naturally curious about the clones and lets them out of the room where Beakley locks them for safekeeping. Huey, meanwhile, struggles with the failure of the raid against F.O.W.L. that he planned, even snapping at Beakley, who refuses to answer him or Scrooge regarding what she knows about F.O.W.L. Webby shows May and June her room, and the family board, but the two are quick to contradict her statements about her "found family", and question her about her real relatives. Webby admits that she knows next to nothing, only for Lena and Violet to walk in just as June is tampering with the board. Lena snaps, and June runs off in apparent tears, making Webby angry at her friend; after going to look for her clone "sister", Webby runs into Beakley.
When questioned, Beakley claims that Webby's parents were an artist and a librarian, and that she only left behind her life as a spy after they passed so that she could raise Webby. Dewey and Louie, meanwhile, are caught up in the series finale of Ottoman Empire, while Della has a heart-to-heart with Donald about his imminent trip. After confessing her feelings about not wanting him to leave, the two siblings share a hug, and then Della decides to go shopping with Donald in preparation for the trip. June, sneaking onto Donald's Houseboat, then seizes the Sword of Swanstantine left there by Della, and is spotted by Huey. When he tries to inform his brothers and Webby, Webby doesn't believe him and is hurt, but soon finds confirmation of his words as she finds May stealing the Blessed Bagpipe of Clan McDuck.
Scrooge tries to speak to Beakley only to find her preparing to leave to face F.O.W.L. alone. He tries to talk her out of it, but she knocks him out before departing. May and June admit that they were tasked with obtaining the last two Missing Mysteries, and that Bradford will only answer their questions once they complete their assigned mission. Webby refuses to go along with them, and May takes the two artifacts while tasking June with subduing Webby. The clone gains the upper hand using the potion Webby took from Black Heron, and seemingly subdues Webby.
Huey comes to apologize to Webby, only to spot the three heading towards a plane Don Karnage has landed outside the manor grounds. He soon follows them and boards the plane unnoticed, while Webby is revealed to have swapped places with June in her own bid to find answers.
Part Two: The Lost Library of Isabella Finch!
Donald and Della get back from their shopping trip, Donald rocking his favored blue sailor suit, only to be crowded by Scrooge, Dewey, and Louie with news of Beakley, Huey, and Webby's absences. Having learned that Huey has left his Junior Woodchuck Guidebook behind, Donald is convinced that this is not an attempt by the family to make him stay, and becomes determined to join in one final adventure.
The disguised Webby arrives at the Library of Alexandria, and discovers that Huey has stowed away with them. Still masquerading as June, she leads her "prisoner" into the F.O.W.L.-controlled library, where May is tasked with bringing Huey to Bradford's office. Back at the manor, Scrooge prepares to leave to confront F.O.W.L. aboard the Sunchaser, and makes a brief attempt to stop Dewey, Louie, Lena, Violet, B.O.Y.D., and Gosalyn from coming along. He soon relents, and the six join him, Donald, Della, Launchpad, Drake, Fenton, Gyro, and Manny aboard the plane.
Huey arrives in Bradford's office, and is stunned to learn that Bradford was in fact the first of the Junior Woodchucks, being the grandson of Isabella Finch. He claims that he only wants to catalogue the Missing Mysteries and complete what his grandmother started, and that Huey and he share the same goal. Meanwhile, Webby drags June to a prison cell, running into Steelbeak, Pepper, the Phantom Blot, and Rockerduck along the way. From Pepper, she learns the location of the F.O.W.L. archive.
The Sunchaser arrives at the library, and Scrooge's team parachutes down, only to scatter in various directions, with Scrooge and his niece and nephew facing a horde of Eggheads. Gyro and Manny run into Pepper and the Blot, the latter of whom has a trapped Gene in his gauntlet. Gyro is swiftly subdued, while the Blot confronts Manny, aka "the Headless Man-Horse of the Apocalypse", who gains the ability to speak and is petrified after being zapped with the Blessed Bagpipe. Launchpad, in company with Darkwing and Gizmoduck, becomes disheartened to think that he's not fit to be with the two heroes. The three are then confronted by Steelbeak, who alerts Don Karnage to the fact that the kids are still aboard the Sunchaser before attacking.
Dewey and Louie find the courage to take action, and have Lena drop her magical concealment of the plane only to be attacked by Karnage, who is eager to finish his feud with Dewey. Bradford convinces Huey to hand over Finch's journal, which Bradford then adds to the original Junior Woodchuck Guidebook while still trying to sway Huey to his side. Scrooge, Donald, and Della prove more than a match for the Eggheads, but face a more difficult challenge when Rockerduck ages Jeeves back to his massive adult size. Having deposited June in a cell, the disguised Webby enters the F.O.W.L. archive room and begins looking through the records. She discovers that May and June were created using a feather taken from her in Istanbird, the Stone of What Was and water from the Fountain of the Foreverglades, and then discovers a folder labeled "April".
Inside that said folder shows a video of Beakley breaking into a F.O.W.L. lab years earlier, but Webby is interrupted by Black Heron before she can learn more. Steelbeak continues to battle Darkwing and Gizmoduck, and turns the Intelli-Ray on himself to boost his intelligence. The move allows him to overpower Drake and Fenton, stripping the latter of his armor before throwing them both into a cell. Bradford then attempts to convince Huey to persuade Webby to voluntarily assist them, but after he's called away Huey spots Pepper taking Gyro to a prison cell. He soon discovers that Gyro's cell is neighbored by many more, with Gyro's closest neighbors being Gandra Dee and Ludwig Von Drake, whom Bradford apparently captured years ago and stopped aging due to being forced to help Bradford with his plans.
Ludwig soon sets Huey straight, informing him that Bradford hates adventure due to his childhood experiences, and is eager to get rid of it forever. Gandra explains that Bradford has used the Solego Circuit to create a void intended to destroy everything-and everyone-associated with adventure, and Huey sees that Bradford has many more captives in his power. Huey leaves to warn his family, only to be stopped by Bradford and thrown into a cell with the others. Scrooge, Donald, and Della struggle against Jeeves, but defeat him with the surprise aid of an Egghead who turns out to be a disguised Beakley. Unfortunately, just as Scrooge has informed Beakley that F.O.W.L. has Webby, they pair are attacked and subdued by May and Black Heron.
Pursued by Don Karnage, pilot Dewey decides to take his own approach and engages the Sky Pirate in a game of chicken, scaring him into turning but causing both their planes to crash land after the engines are disabled. The disguised Webby is then tasked with interrogating Beakley, with the Lost Harp of Mervana acting as a lie detector. Beakley reveals that she found Webby as an infant in F.O.W.L.'s old headquarters years ago, and took her in and brought her to McDuck Manor so she could grow up safe and happy. Unfortunately, Beakley's confession makes her realize the depth of her "grandmother's" deception, and Webby reluctantly agrees to help Bradford, her creator, as she was intended to calling her by her real name, April.
Part Three: Tale's End!
Outside the library, the other kids awake, and Lil Bulb attaches B.O.Y.D.'s head to his body, B.O.Y.D. having become separated from the rest of his body in the crash. The six then head into the library, where Bradford leads Webby to a mysterious walkway overlooking the expansive structure. Her presence causes the Papyrus of Binding to emerge from a mysterious box, but it becomes blank before she can see what's written on it. Bradford then seizes the artifact, revealing that obtaining it was the whole purpose of Webby's creation in the first place.
Scrooge awakens tied to a chair and is approached by Bradford, who notes that Scrooge's other friends and relatives have similarly been captured. Meanwhile, Lena and Violet find the Blot attacking Manny, who is supposed to bring about the end of the world but apparently has no desire to do so. Assuming her sorceress form, Lena comes to Manny's aid, freeing Gene and allowing Manny to assume his true demonic winged form. Steelbeak continues to pound on a helpless Launchpad, with Darkwing and Fenton unable to aid him and the Gizmosuit inactive. Fortunately, Gosalyn and B.O.Y.D. appear to help their superhero friends, while elsewhere Dewey and Louie follow a sign left by Huey and manage to free him from his cell with some assistance from Gyro.
Unfortunately, the three are soon captured by May and June disguised as Webby's silhouette. Meanwhile, Bradford explains to Scrooge his origins and desire to rid the world of adventure, and noting that everything to do with adventure from the past hundred years also has to do with Scrooge. Bradford reveals that he wants to make a deal with Scrooge, who breaks free from his bonds and attacks. However, Bradford gains a set of mystical armor from the Sword of Swanstantine and fights back. The boys and Huey's cell neighbors are then tied up in a room with Webby, while Steelbeak continues to terrorize Launchpad's team. Fenton instructs B.O.Y.D. to get the armor back online, while an outmatched Steelbeak reveals that he has altered the Intelli-Ray to turn its victims into zombies.
Gosalyn and Launchpad are set upon by the affected Flintheart Glomgold, Ma Beagle, and the Original Classics. Lena, Violet, and Manny arrive to aid them, only to be blasted by a zombified Magica, and are soon thrown into a cell. B.O.Y.D. and Gosalyn are also subdued, leaving Launchpad alone against Steelbeak and his minions. Scrooge and Bradford battle through the library, and Bradford manages to goad Scrooge into a foolhardy attack by revealing that he is the one who leaked the existence of the Spear of Selene to Della. Arriving on the library roof, Scrooge sees Beakley, Donald, and Della captive and learns that the boys and Webby have also been captured.
Bradford offers Scrooge a deal: he can return home with his family, but only if he signs a contract written on the Papyrus of Binding to never adventure again. When Scrooge points out that getting rid of adventure would mean disposing of his own personnel, Bradford callously throws the rest of the Board of Directors and Black Heron into the Solego Vortex. Huey, viewing the conversation through a video call, accuses Bradford of lying, as only Scrooge's heir can find the papyrus. When Webby admits that she found it, Ludwig reveals that as May and June were cloned from her, she was cloned...from Scrooge.
Having learned that their only reason for being was to help Bradford get the last artifact, May and June are hurt and frustrated, but are persuaded to help free Webby and the others to save the family, which they are now a part of. Launchpad, at Steelbeak's mercy, feels despondent, not believing himself to be a hero. However, his captured friends, including Penumbra, the Rescue Rangers, and various other hostages of F.O.W.L., voice their belief in him. With their vote of confidence, Launchpad dons the Gizmoduck armor, and soon terrifies Steelbeak into fleeing before accidentally freeing his friends.
Scrooge, needing a strategy, attempts to delay his signing of the contract, but Bradford threatens to throw Donald into the vortex so Scrooge reluctantly gives in and signs the contract. Now constricted by magical chains, he watches as Bradford prepares to throw in Donald anyway, only for the vortex to deactivate as Scrooge's rescued allies arrive. Furious, Bradford goes after Scrooge but is stopped by Webby, who tells the Buzzard to "Get away from my dad!" much to Scrooge's shock. As the heroes try to save Scrooge, the Sword of Swanstantine amplifies Bradford's inner evil into an increasingly monstrous form. He attempts to blast the still defenseless Scrooge, but Donald puts up a barrier and is joined in holding it by Della, Webby, Dewey, Beakley, and the reformed May and June.
Huey and Louie analyze Bradford's contract, and discover a loophole: it says Scrooge can have his family if he gives up adventure; however, as the McDucks always say, "family is the greatest adventure of all". The contract disintegrates, losing its validity, and Bradford loses the sword and is left powerless, fleeing only to find Magica, Glomgold, and the Beagles waiting for him. Magica then turns him into an ordinary Buzzard, and Scrooge's adversaries then depart rather than face his family, both genetic and found. Scrooge and Webby, now knowing the truth about their relation to each other, embrace, and are soon joined by Beakley, whom Webby forgives, and the rest of the family piling on to them.
As the whole group head back home aboard the Sunchaser, May and June are officially welcomed to the group, with Donald calling Daisy to see if she'd be okay with a couple more passengers on their trip. Scrooge, proving as overprotective a father figure as his nephew, is calmed by the assurances of his great-nephews and newfound daughter. Launchpad, thrilled by the group's success, leaves the controls to grab the Ducks in a group hug, with Della thankfully taking over steering before they can crash. Relieved not to have made an even bigger mess, Launchpad accidentally hits the button to open the cargo door, sending the entire group flying out the back of the plane. Of course, the heroes soon turn it into an unexpected free fall into a skydive through the end credits, only proper for a family of adventurers.
- David Tennant as Scrooge McDuck
- Danny Pudi as Huey Duck
- Ben Schwartz as Dewey Duck
- Bobby Moynihan as Louie Duck
- Kate Micucci as Webby Vanderquack
- Tony Anselmo as Donald Duck
- Paget Brewster as Della Duck
- Beck Bennett as Launchpad McQuack
- Toks Olagundoye as Mrs. Beakley
- Keith Ferguson as Flintheart Glomgold, Johnny, Randy, Frankenjeeves, Eggheads
- Jim Rash as Gyro Gearloose, Gizmoduck Armor
- Marc Evan Jackson as Bradford Buzzard, Bentley and Buford Buzzard
- Riki Lindhome as May (debut)
- Noël Wells as June (debut)
- Kimiko Glenn as Lena
- Libe Barer as Violet
- Chris Diamantopoulos as Drake Mallard/Darkwing Duck, Storkules, Eggheads
- Stephanie Beatriz as Gosalyn Waddlemeyer
- Lin-Manuel Miranda as Fenton Crackshell-Cabrera/Gizmoduck
- Jason Mantzoukas as Steelbeak/Steelbrain
- Jameela Jamil as Gandra Dee
- Margo Martindale as Ma Beagle
- Giancarlo Esposito as Phantom Blot
- Amy Sedaris as Pepper
- Tress MacNeille as Daisy Duck
- Paul F. Tompkins as Gladstone Gander
- Jaime Camil as Don Karnage
- John Hodgman as John D. Rockerduck
- April Winchell as Black Heron, Eggheads, Rescue Rangers
- Tom Kenny as Fethry Duck, Eggheads
- Keith David as Manny
- Catherine Tate as Magica De Spell
- Julie Bowen as Penumbra
- Jaleel White as Gene the Genie
- Retta as Harp
- Corey Burton as Ludwig Von Drake, Rescue Rangers
- Eric Bauza as Beagle Boys
- David Kaye as Duckworth
- Noah Baird as B.O.Y.D.
- Arturo Del Puerto as Panchito Pistoles
- Bernardo de Paula as José Carioca
Molly Cunningham, Kit Cloudkicker, Goldie O'Gilt, Santa Claus, Selene, Zeus, Strongbeard, Black Arts Beagle, Hortense McDuck, Bombie, Hack and Slash Smashnikov, Gabby McStabberson, Mark Beaks, Doofus Drake, Doofus's parents, King Honestus, Aletheia, Vero, Gavin, Zan Owlson, Downy McDuck, Fergus McDuck, Matilda McDuck, Officer Cabrera, Faris Djinn, Roxanne Featherly, Gibbous, Akita, Amunet, Jane, Timmy Jenkins, a clown, and a dog (among many others) appear, whether fully animated, in pictures, or as silhouettes, but have no lines.
- This special is the only multi-part DuckTales story to have three parts; Woo-oo!, The Shadow War!, Moonvasion!, and Let's Get Dangerous! each only had two.
- Webby's updated board includes the following information she has been collecting:
- The McDuck/Duck family tree, so far as Webby is aware of it.
- A section on Money Bin employees in the top left corner, with the personnel of Gyro's lab circled and labeled "Team Science". Nearby are pictures of Quackfaster and Gandra, with a note not to tell anyone that Fenton is Gizmoduck.
- Pictures of Amunet and Faris Djinn in the top right corner.
- "Project87" may be a reference to the premiere date of DuckTales 1987.
- Ironically, there was a DuckTales 1987 episode titled Scrooge's Last Adventure which was one of the show's final episodes.
- The Library of Alexandria is a real world location, which was destroyed multiple times many centuries ago. This Library was also an important location in the Don Rosa story, The Guardian of the Lost Library.
- In revealing that he told Della about the Spear of Selene, Bradford proves himself to be a hypocrite. In Let's Get Dangerous!, he had berated the Duck family's adventuring, claiming it was the cause of the events of The Shadow War! and Moonvasion!, but both of these events indirectly occurred due to Della's disappearance, giving him some level of responsibility for both attacks.
- This is the second ungated episode of DuckTales 2017 featured on Disney Now with the first being "Let's Get Dangerous!".
- During the battle against FrankenJeeves, Scrooge uses his cane like a Pogo stick which is a callback to the DuckTales video games (DuckTales, DuckTales 2, and DuckTales Remastered).
- In some of Donald's luggage, there's a shirt that resembles his Hawaiian floral print shirt from "Quack Pack!"
- This is further justified when Della asks Donald if this is 1996, a reference to the show's airing.
- Another tidbit is that a "hidden Mickey" can be seen on the shirt's tag.
- The tune played during Webby's birthday party is the series' theme song.
- The F.O.W.L. spy-bot used to spy on the family at Funso's resembles Sebastian from The Little Mermaid.
- When infiltrating F.O.W.L. headquarters, Dewey says: "Come with me if you want Dew live."; a reference to one of the Terminator's famous quotes from the Terminator franchise.
- Then Huey opens the original Junior Woodchuck Guidebook, on its pages can be seen pictures of objects from famous action-adventure movies: Meerschaum pipe of ship Charlotte and Eye of Providence from National Treasure, Key to Book of the Dead and scarab beetle from The Mummy.
- Manny being voiced by Keith David, his turning to stone, and the music that plays as he transforms into a winged, demonic horse, are all references to Gargoyles.
- Ludwig Von Drake sings a rendition of The Green With Envy Blues while in his cell.
- When Bradford enters the interrogation room and says "Correct", he imitates the Lost Harp of Mervana.
- Webby being Scrooge's cloned daughter is reminiscent of the plot of the Doctor Who episode "The Doctor's Daughter", in which Scrooge's voice actor David Tennant portrayed the Tenth Doctor.
- Launchpad is the last character in the series to speak (not counting everyone's screaming as they fall off the Sunchaser/Cloud Slayer), while Scrooge, Huey, Dewey, Louie, and Webby were the last characters to be seen in the series.
- Goof: During Webby's "Birthday Party" at Funso's Daisy is seen with her shoes on but when the McDuck Clan and their friends begin their plan to found F.O.W.L'S base, she's webbed-foot.
- The credits scene where all the characters involved in the battle against F.O.W.L fall out of the plane is similar to the Season 3 poster.
- Launchpad speaks the series' last line: "Whoa! Alright! That was close, Launchpad. Phew, almost ruined the tender-family moment."
- Because Disney Channel Asia ceased operations for most of its channels, including Nat Geo & Nat Geo WILD, (or in other words, because of Disney+), this is not only the final DUCKTALES episode, but ALSO the final movie to air on Disney Channel Asia.