In a quiet neighborhood in Brooklyn, a young playwright named Mortimer Brewster returns home to announce his engagement to the beautiful Elaine. However, what seemed like a perfect day turns into a comic nightmare when Mortimer discovers that his family, particularly his lovely aunts Abby and Martha, have a dark secret: they are poisoning lonely elderly men who come to their home, offering them a "haven" filled with love... and arsenic. As he tries to process this revelation, Mortimer becomes caught in a whirlwind of absurd situations involving his insane brother Teddy, who believes he is President Theodore Roosevelt, and a dangerous cousin who has escaped from the asylum.
As the entanglements increase and bodies begin to pile up, Mortimer struggles to maintain his sanity and keep the police out of it, all while trying to keep his relationship with Elaine afloat. Confusion escalates when Mortimer's attempts to handle the crazy situation lead to hilarious scenarios and misunderstandings that surpass any play he could write. With a dark sense of humor and a plot full of twists, the story turns what should be a family celebration into uncontrolled chaos, where the line between madness and sanity blurs even further in this comedy classic.