"Never Bet the Devil Your Head" is the sad history of the short life of the narrator's friend, Toby Dammit. Dammit had many vices, all of which resulted from a personal defect of his mother. Her defect was her being left-handed. As a result, she flogged her child from left to right, which is in opposition to the revolution of the world. "If each blow in the proper direction drives an evil propensity out, it follows that every thump in an opposite one knocks its quota of wickedness in."
As a result of these frequent beatings, Toby developed a propensity for cursing and swearing, and for backing his assertions by bets. As he was a very poor boy, Toby's bets were never taken seriously by those around him. As time went on, Toby abandoned all forms of real wagering, and began using the expression "I'll bet the Devil my head" whenever he felt the urge to bet.
One day, the narrator and Toby were walking across a covered bridge. The bridge had few windows and was therefore quite dark. Near the end of the bridge, the two encountered a turnstile. Toby insisted on leaping the stile and said he could cut a pigeon wing over it. The narrator doubted Toby's ability, and Toby then bet the Devil his head that he could do it. As soon as Toby pronounced the words of the bet, a "little lame old gentleman of venerable aspect" appeared and lay the ground rules for Toby's jump.
Finally, Toby started running and lept into the air just prior to reaching the turnstile. In the middle of the jump, Toby fell flat on his back, and the old man limped quickly away with something in his apron. The narrator rushed over to...