Scrooge, Della, and the kids manage to reach the Money Bin, only to learn from Gyro that the Moonlanders have taken out all their contingency plans. Lunaris then broadcasts to the city, declaring the Moonlanders' superiority as he seemingly lands a massive ship atop Killmotor Hill. Knowing that the boys are among his targets, Scrooge and Della secretly agree to get them to safety. While Gyro sends Lil Bulb and several duplicates to gather allies from across Duckburg, Della takes the kids in the Cloudslayer on the pretext of recruiting allies from around the globe.
Back in Duckburg, Scrooge leads his forces into battle, and charges ahead with Launchpad and Darkwing while the others hold off the Moonlander guards. The heroes call in additional allies, including the Harpies and several clones created by Gyro. Arriving at Ithaquack, the Ducks learn that Zeus has grounded Selene and Storkules, and refuses to allow the group in despite Della's pleas. As the kids question Della's actions, a Moonlander ship arrives to attack, forcing them to flee in the Cloudslayer.
In Duckburg, Scrooge switches outfits with Darkwing, who with Launchpad deals with security on the lawn of McDuck Manor. Scrooge infiltrates the manor itself, and gets to the entrance ramp of Lunaris' ship only to find that it's a giant hologram. Lunaris then reveals that he predicted Scrooge's actions, and demonstrates the capture of most of Scrooge's allies and the Cloudchaser being shot down. He then lands his true flagship, a Planetary Engine designed to cause the Earth to begin orbiting the moon.
Della and the kids find themselves stranded on an apparently deserted island, only for Donald—scruffy and accompanied by a ventriloquist dummy melon—to emerge from the undergrowth.
Donald and Della, recognizing each other, are initially furious, Della for Donald's long absence and Donald for Della not getting his message. Despite this, the two siblings embrace, and the kids are quick to conceal the fact that they were unaware of Donald's going missing. However, when they suggest finding a way back home, Della admits that she took the kids away from Duckburg to keep them safe. Meanwhile, Duckburg begins to freeze over due to Lunaris' engine moving the Earth, and Scrooge assembles at Chum's with Beakley, Manny, Launchpad, and Duckworth, his last remaining allies.
Duckworth soon ditches the group and heads to the afterlife to "prepare places for them", while Scrooge is at a loss as to how to defeat Lunaris. Unlikely—and unwelcome—help appears in the form of Flintheart Glomgold, whom Scrooge realizes may actually be the key to victory. Back on the island, Della attempts to convince her family to stay on the island, but upon realizing that she feels stranded as she was on the moon kicks Donald's melon into the ocean in a rage. Louie then approaches her and, after rekindling her fighting spirit with her lullaby (which Donald shared with the boys), the Ducks are startled by some unexpected arrivals: Fethry, Gladstone, and Mitzy with the Gladyear Blimp.
Back in Duckburg, Scrooge and his few allies put up with Glomgold's inane plans, having no real alternatives. The scheme calls upon Beakley—dressed as a child—to operate a giant slingshot to fire Launchpad—dressed as a rock—into Lunaris' flagship. Having dressed several of his pet sharks in parkas, Glomgold sends them in under the iced over Audobon Bay to attack the supports of Lunaris' ship. Much to Scrooge's chagrin, he is sent to distract Lunaris by driving a Manny-drawn sleigh...dressed as Santa Claus.
After catching up, Fethry and Gladstone carry their cousins and the kids back towards Duckburg aboard Mitzy. In Duckburg, Lunaris catches on to Glomgold's plan and is baffled, particularly as Scrooge and Glomgold begin quarreling in front of him. As the sharks and Launchpad accomplish their task, the two rivals and Manny engage Lunaris in a hand-to-hand battle. Despite their brave efforts, Lunaris emerges on top, only for Mitzy to arrive and join in the attack.
Gladstone's luck helps take out the last support holding up Lunaris' Planetary Engine, which begins to tumble as Lunaris scrambles back inside. Taking advantage of its still active thruster, Mitzy catches the falling craft and aims it back towards the moon. Unfortunately, Lunaris regains the controls and, determined to achieve victory, decides to destroy the Earth if he cannot conquer it by ramming his ship through the core. Seeing this, Della boards a nearby Spear with Donald, Scrooge, and the kids.
With the kids acting as gunners and Donald and Della fighting over the controls, the Ducks attempt to halt Lunaris' flagship. Unfortunately, his final line of defenses proves too much, and all hope seems lost. However, Penumbra then appears in the original Spear of Selene and crashes into Lunaris' last engine, crippling his ship, and is picked up by Della and her family. Glomgold's sharks have eaten away at the ship's circuitry and Selene then appears on Lunaris' bridge and informs him, to his dismay, that not only has Storkules gotten Earth back into orbit, but his flagship has become a second moon.
Back on Earth, the freed citizens of Duckburg and the heroes gather in celebration of their victory. Launchpad becomes smitten with Penumbra, and the Ducks are confident that they can face any future difficulties as a family. Unbeknownst to them, they are being observed by the Board of Directors, who prove to be the High Command of F.O.W.L. Having grown tired of Scrooge and his family threatening their schemes, the group—including Gandra Dee, Jeeves, a cryo-frozen Rockerduck, Steelbeak, the Phantom Blot, and Black Heron—set out to eliminate them once and for all.
This is the second time the title sequence rolls before the episode begins.
Scrooge references his great-grandfather. He also paraphrases the Scottish proverb "Twelve Highlanders and a bagpipe make a rebellion."
Donald's melon, besides being an obvious reference to the Tom Hanks film Cast Away, is in the shape of Mickey Mouse; this is further emphasized by it being "voiced" by Chris Diamantopoulos, one of Mickey's current voice actors, and its use of several of Mickey's signature phrases. Furthermore, the melon and its place on a desert island are reminiscent of the Watermelon Stevens living on Mask Island in the Cartoon Network animated series Steven Universe.
A rendition of the Moon Stage Theme can be heard during the duck family and Lunaris spaceship battle.
Dewey revealed that he and his brothers are eleven years old; the triplets' age had never been mentioned specifically before now. However, Scrooge noted in "The Last Crash of the Sunchaser!" that the boys were hatched shortly after Della's disappearance, and various episodes indicated that Della was trapped on the moon for approximately ten years.