The story unfolds with Mortimer Brewster, a recently engaged drama critic, who returns to his childhood home in Brooklyn to introduce his fiancée, Elaine Harper, to his eccentric family. Upon arrival, Mortimer is shocked to discover that his sweet, elderly aunts, Abby and Martha Brewster, have been discreetly killing lonely old men by serving them elderberry wine laced with arsenic. They believe they are performing a charitable deed by "relieving" these men of their suffering. Mortimer, in disbelief, becomes even more flustered when he finds out they keep the bodies in the basement. Adding to his distress is his brother Teddy, who lives with the delusion that he is President Theodore Roosevelt. Teddy assists in burying the bodies, convinced he is digging locks for the Panama Canal.

Amidst this chaos, Mortimer is further plunged into disarray as his other brother Jonathan returns home with a new face after having undergone plastic surgery to disguise himself from the law. Jonathan, a violent criminal, arrives with his sinister alcoholic accomplice, Dr. Einstein. As tensions mount, Mortimer desperately tries to put an end to his family's insanity and shield his beloved Elaine from discovering the truth. Navigating through a tangled web of deception, hidden bodies, and threatening behavior, Mortimer races against time to find a solution to his ever-growing list of familial problems. With everything at stake, Mortimer must now manage his family’s peculiarities while ensuring his own sanity remains intact.