When Scrooge unexpectedly disappears during his birthday party, Huey, Dewey, and Louie find themselves hosting a mystery party where everyone is a suspect.
Bentina Beakley, Webby, and Donald are leaving the manor for the weekend, for Beakley and Webby it is for a training expedition. When Huey, Dewey, and Louie ask why everyone's in a hurry to leave, Beakley explains that it is Scrooge's birthday, which he does not like celebrating after his beloved butler Duckworth passed away. Shocked that Scrooge doesn't like his birthday, Huey is eager to cheer up Scrooge by throwing him the best birthday he could have.
Scrooge is incensed to find himself dragged into a surprise party the boys have put together. However, seeing Huey ask to try enjoying it, Scrooge begrudgingly resigns himself to the party with a lukewarm reception. Then, an illusionist named Nik Nokturne Louie hired gets Scrooge to be a volunteer in his magic act, a spirit summoning. During the performance, the lights suddenly go out as a mysterious voice wails. When the lights come back on, Scrooge is gone and everyone is locked in.
Panicking, Huey surmises that one of the guests is Scrooge's kidnapper and resolves to keep the birthday going as a "mystery party" to catch the culprit. After investigating the crime scene, the boys discover that Nik is actually Black Arts Beagle, a Beagle Boy who infiltrated the party with Ma Beagle to steal the deed to Duckburg from Scrooge. However, Ma denies kidnapping Scrooge. Huey notices the electrical system was hacked and discovers another guest is Mark Beaks, except Beaks didn't kidnap Scrooge and only came to get humiliating footage of Scrooge from the surveillance systems. Beaks did record footage in the blackout, which reveals Flintheart Glomgold as the last guest trying to sabotage the magic act. Glomgold, however, is also not the culprit. Huey begins to accuse Ma Beagle, Beaks, and Glomgold when the lights go out again, and the villains disappear. With no clue of who the culprit is, Huey accuses Dewey and Louie of sabotaging the party but Louie argues that they worked hard on the party and they're receiving no gratitude on Huey's end. While arguing, none of them notice Black Arts summoning a demon.
Revealing himself to be an authentic magician, Black Arts confesses to the kidnapping as revenge for Ma Beagle's neglect of him. Black Arts then commands the demon to attack, but the demon turns on him and causes Black Arts to vanish. After the triplets escape, Huey realizes who the culprit is. He leads his brothers to the surveillance room to reveal Scrooge's kidnapper - Scrooge himself. Huey explains that only someone who hates parties like Scrooge would want to sabotage their birthday, which helped him figure out Scrooge was behind his disappearance. Scrooge adds on that he had help from a ghost, specifically the demon Black Arts summoned, who turns out to be the ghost of Duckworth. Black Arts had unintentionally summoned Duckworth during the magic act, so he hid Scrooge to protect him and removed the villains from the manor. Huey accepts Scrooge's preferences and promises not to throw any celebrations if Scrooge doesn't want them.
Webby and Beakley return home the next day and Duckworth's ghost is there to greet them. Duckworth dryly criticizes Beakley's housekeeping, prompting Beakley to groan she liked it better when Duckworth was not around.
- David Tennant as Scrooge McDuck
- Danny Pudi as Huey Duck
- Ben Schwartz as Dewey Duck
- Bobby Moynihan as Louie Duck
- Tony Anselmo as Donald Duck
- Kate Micucci as Webby Vanderquack
- Toks Olagundoye as Bentina Beakley
- Margo Martindale as Ma Beagle
- Eric Bauza as Nik Nokturne/Black Arts Beagle
- Josh Brener as Mark Beaks
- Keith Ferguson as Flintheart Glomgold
- David Kaye as Duckworth
- McDuck Manor's electric system is labeled "DT-87", referencing 1987's DuckTales.
- Duckworth (in demon form) is revealed to be the spirit seen in the theme song.
- Dewey's costume is a reference to Daft Punk. His keytar may be the same as Randy Cunningham from Randy Cunningham: 9th Grade Ninja; both characters are voiced by Ben Schwartz.
- The word search contains the following:
- GLASGOW - a reference to Scrooge's birthplace
- THE BUTLER
- DID IT
- The above two reference the phrase "the butler did it", a mystery trope where the butler turns out to be the culprit as no one would suspect it was them. It also foreshadows Duckworth was behind Scrooge's disappearance.
- KLONDIKE - a reference to "Back to the Klondike" and the story of the same name.
- YUKON - a reference to North of the Yukon.
- GOLDEN SUN - a reference to "The Treasure of the Golden Suns".
- BARKS - a reference to Carl Barks.
- When Louie tries to justify inviting Ma Beagle to the party, Huey reveals that two months have passed since the events of "The Beagle Birthday Massacre!"