In his detecting debut, larger than life lexicographer Dr. Gideon Fell is entertaining young American college graduate Tad Rampole at Yew Cottage, Fell's charming home in the English countryside. Within sight of his study window is the ruin of Chatterham Prison, perched high on a precipice known as Hag's Nook. The prison's land belongs to the Starberth family—whose eldest sons must each spend an hour in the prison's eerie "Governor's Room" to inherit the family fortune.

Rampole is especially interested in the family, having met the young and beautiful Dorothy Starberth on the train from London. He readily agrees when Fell and the local reverend, Thomas Saunders, ask him to accompany them as they watch and wait for badly frightened Martin Starberth to complete 'his hour' in the prison. Martin has every reason to be afraid; more than one Starberth heir has met an untimely end. Will his turn come tonight?