William Marble is a bank clerk living in south London, desperately worried about money and unable to control his wife Annie's spending. One evening without warning they are visited by his recently orphaned and very rich young nephew, James Medland, who has a large amount of cash on him. Unable to resist the opportunity put in his way, William Marble sends his wife to bed early that night, saying that he wants to talk business and suggests she pleads a headache so as not to seem unsociable. He then slips poison in his nephew's drink, the latter dies and William buries him in the back garden under cover of darkness that night.
Some lucky speculation on the stock exchange with his ill-gotten gains brings William Marble untold fortune. Annie assumes at first that her husband was given or lent the money by James, and she says that now they can afford it, she wants them to move to a better house with an attractive garden. He is unable to move for fear of anyone discovering the terrible secret, and his character is transformed by what he has done. Eventually she stumbles on the terrible truth, and the result brings unforeseen misery for them and their son John. There is an unexpected twist at the end.