Markheim is in a store wishing to buy a Christmas present for a woman he is going to marry. The store clerk shows him a mirror. Markheim is scared of his reflection. Markheim isn’t sure if he wants to buy it, but the clerk says he must buy it or leave. Markheim just decides to go look at more items. The clerk turns his back to put away the mirror, and then Markheim pulls out a knife and stabs him to death. Markheim spends some time recovering when he hears someone moving about upstairs. He knew no one else was there so he reassures himself that the outer door is locked.
He searches the dead body for keys and goes upstairs where the clerk lived to look for money. As he searches, he hears footsteps walking up the stairs and a man opens the door and asks, “Did you call him? ” Markheim at this point believes the stranger is the Devil. Though he never identifies himself, the stranger is clearly supernatural; he says that he has watched Markheim his whole life. He tells Markheim that the servant has left her friends early and is returning to the store, so Markheim better hurry. Markheim stoped looking for money and tries to explain his life and behavior to the stranger, entering into a discussion of good and evil.
Markheim admits that he has thrown his life away and turned to evil. The servant returns, and as she knocks on the door the stranger advises Markheim that he can lure her in by telling her that her master is hurt, then kill her and have the whole night to rob the house. Markheim replies that if he has lost the love of good, he still hates evil, and can still do one worthwhile thing by ending his life. At the end of the conversation, he refuses to kill the maid and continue robbing the house. The stranger then disappears. Then Markheim opens the door and tells the servant, “You had better go for the police; I have killed your master. “