review a play, he makes the aunts promise not to take any action until he returns, including burying the body. They agree but remain clueless about why Mortimer is behaving so strangely.

After Mortimer departs, Jonathan arrives with Dr. Einstein. The aunts fail to recognize their nephew, prompting Jonathan to explain that Dr. Einstein has surgically altered his face. Once Jonathan proves his identity, he tells them he has come from Chicago, where he and the doctor were working together. As the visibly nervous aunts retreat to the kitchen, Einstein asks Jonathan what their next move should be, mentioning that the police are pursuing them for murder and that they have a dead body in their car. Jonathan confesses that he killed Mr. Spenalzo because the man remarked that he resembled Boris Karloff after Einstein's surgery.

Upon the aunts' return, they inform Jonathan that he must leave, reminding him that he was never content in the house. Jonathan, however, persuades them to let him and Einstein stay for dinner. Discovering that his grandfather's laboratory is still upstairs, Jonathan decides the house would be an ideal operating room for Einstein to work on disguising criminals, including himself. He reassures Einstein that the aunts won't be able to force them out. The act concludes with the two men being startled by Teddy's bugle blast as they rush upstairs.

Act 2

After dinner, the aunts renew their attempts to make Jonathan leave. He warns them about how "disagreeable" he was as a child, hinting that it "wouldn't be pleasant for any of [them]" if they tried to force him out. He tells the aunts about his plans for the grandfather's laboratory, which they immediately refuse. However, they agree to let him stay for the night. During this discussion, Einstein goes with Teddy to the basement to "inspect the locks in Panama." Upon returning upstairs, Einstein tells Jonathan he has found a place to bury Mr. Spenalzo, revealing that Teddy has dug a hole in the basement.

As Jonathan and Einstein move their car to the back of the house, the aunts decide to bury Mr. Hoskins, who remains in the window seat, once the men go to bed. When the house is quiet, Teddy carries the body to the basement. Shortly thereafter, Jonathan and Einstein bring in Mr. Spenalzo's body, placing it in the window seat when they hear Elaine knocking. She initially thinks they are burglars until Jonathan reveals his identity. Believing she witnessed them carrying the body, Jonathan forces her into the cellar. Her screams bring the aunts downstairs, dressed for Mr. Hoskins’s funeral.

Elaine manages to escape just as Mortimer arrives. Jonathan and Mortimer argue until the aunts insist they all settle in for the night. Later, when Elaine demands to know what's happening in the house, Mortimer tells her they cannot marry because insanity runs in his family. Upon seeing Mr. Spenalzo's body in the window seat instead of Mr. Hoskins's, he convinces Elaine to go home.

The aunts are perplexed by the identity of the new corpse in the window seat. When Mortimer realizes the body is linked to Jonathan, he attempts to coerce his brother into leaving. Jonathan, however, refuses and threatens Mortimer with the same fate as Mr. Spenalzo. Just then, Officer O’Hara arrives, curious about the lights being on so late. Mortimer, relieved to see the officer, persuades him to stay until Jonathan departs. O’Hara is happy to oblige, as it gives him a chance to discuss the play he's been writing.

Upon discovering Mr. Hoskins’s body in the cellar, Jonathan threatens to inform O’Hara. Mortimer then convinces the officer that he will meet him later to discuss the play. The aunts confess to Jonathan that they have twelve bodies in the basement. This revelation wounds Jonathan’s pride, as Einstein notes that the aunts have killed as many men as Jonathan has. Consequently, Jonathan decides to murder Mortimer to tip the balance in his favor.

Act 3

Later that evening, as Jonathan and Einstein are interring Mr. Spenalzo with Mr. Hoskins in the cellar, Mortimer returns with a doctor’s signature on Teddy’s commitment papers. He tells the aunts that he can only protect them if Teddy takes the blame for the murders. They threaten to contact the police if Mortimer doesn't find a way to remove Jonathan by morning.

Jonathan instructs Einstein to fetch his medical tools, planning a slow and painful demise for Mortimer. After binding and gagging Mortimer, they pour two glasses of poisoned wine. Just as they are about to drink, Teddy blasts his bugle, causing them to drop the glasses and spill the wine. Passing by the house, Officer O’Hara hears the blast and enters to complain. Einstein explains that Mortimer is tied up because he was reenacting a scene from a play he saw that evening. O’Hara decides not to untie Mortimer, forcing him to listen to the officer's summary of his play.

By morning, O’Hara is concluding his summary when Brophy and Klein arrive, looking for him. They announce that their lieutenant is determined to send Teddy to Happy Dale due to numerous complaints about the bugle blasts in the night. Jonathan wakes up, sees the officers, and mistakenly believes he’s been caught. When Klein remarks that he resembles Boris Karloff, Jonathan lunges at him but is knocked unconscious by Brophy. Lieutenant Rooney then arrives and identifies Jonathan as a wanted criminal and an escapee from an asylum. None of the officers believe Jonathan when he claims that there are thirteen bodies buried in the basement.

Shortly after Mortimer informs the Lieutenant about Teddy's commitment papers, Elaine and Mr. Witherspoon, the superintendent of Happy Dale, arrive. Mortimer instructs Elaine to "run along home" until he contacts her, but she refuses to leave. Teddy agrees to accompany Witherspoon, believing he will be his guide on an expedition to Africa. When the aunts insist that they must accompany Teddy to Happy Dale, Mortimer concurs, as does the lieutenant, especially after the conversation shifts to the bodies in the cellar.

Once the aunts' commitment papers are signed, they express doubts about the validity of the signatures. They decide to reveal the truth to Mortimer—that he is not a Brewster. They explain that his mother worked as their cook and that he was born out of wedlock. Mortimer and Elaine are thrilled by the news and head to her house for breakfast. Meanwhile, the officers arrest Einstein and Jonathan, with Jonathan feeling satisfied that the aunts won't surpass his murder record. After they leave, the aunts question Mr. Witherspoon about his personal history and discover he has no family. The play concludes with them inviting him to breakfast and offering him a taste of their elderberry wine.