In Act II of Arsenic and Old Lace, Dr. Einstein discovers twelve dead bodies in the cellar. The aunts refuse to let Jonathan bury a stranger with their friends. Angered that his relatives have managed to kill as many as he without even leaving their home, an enraged and insane Jonathan vows to kill a thirteenth. In the meantime, the doctor has followed the descriptions of Mortimer who ridicules the murder dramas he criticizes and ties and gags the equally unsuspecting Mortimer. The doctor and Jonathan are ready to drink a toast to each other with the elderberry wine when Officer Hardy knocks on the door in response to complaints of Uncle Teddy's loud blowing of his bugle. When the policman notices the gagged Mortimer, the doctor explains that Mortimer has merely been dramatizing one of the plays he has criticized. O'Hara begins to describe a play he himself is writing; fortunately, however, Officer Brophy enters and becomes aware that Mortimer is choking. When he loosens the restrains upon Mortimer, Jonathan tells the policeman not to listen to Mortimer because he is dangerous:
JONATHAN That's why we had to tie him up. He's the lowest kind of person in the whole world.
O"HARA A dramatic critic?
When Jonathan tries to tell the police that the aunts are murderers, O'Hara recognizes Jonathan as the murderer who looks like Boris Karloff; Jonathan then tries to choke him to death. But, Brophy clubs him over the head, and they start to drag him to the patrol car, but O'Hara asks, "What about the bodies?" Brophy replies that this statement of Jonathan just shows how crazy he is. Mortimer reminds the policemen of Dr. Einstein who is probably fleeing.
In the meantime, Dr. Witherspoon from the mental asylum, Happy Dale, arrives to pick up Uncle Teddy. Mortimer has arranged for his aunts to accompany Teddy so they can "be close to him." At this news, the aunts are elated, offering Mortimer the house since he is going to marry Elaine. Remembering Elaine is outside, he runs to tell her that insanity runs in his family and he cannot marry her. Just then, Witherspoon notices the elderberry wine; the aunts offer him some and the curtain falls.