The Addams Family must rescue their beloved Uncle Fester from Debbie, a black widow serial killer, who plans to marry him for his wealth and then murder him. Meanwhile, Wednesday and Pugsley are sent to a summer camp where they make enemies with the snobby camp owners and befriend a misfit named Joel. With the help of Joel, they uncover Debbie's true identity and attempt to stop Fester's wedding. After a series of comedic and macabre events, the Addams Family successfully save Fester and defeat Debbie.

Con artists plan to fleece an eccentric family using an accomplice who claims to be their long-lost uncle. Gomez Addams laments the 25-year absence of his brother Fester, who disappeared after the two had a falling-out. Gomez's lawyer Tully proposes that Gordon, who closely resembles Fester, pose as him to infiltrate the Addams household and find their hidden vault. As Gordon grows closer to the Addams family, he begins to question his deception but ultimately turns against the con artists to protect his newfound family. In the end, it is revealed that Gordon is actually Fester who had suffered amnesia after being lost in the Bermuda Triangle.