Jupiter Jones was tall and thin and slightly sunken. When he sat down in a chair it was hard to believe that he would be able to get up again. He did not collapse in a chair, he entwined himself in it. He looked as though he had just come out of a hospital after a lingering illness, but he could play five sets of tennis in a midsummer sun. He was a physical contradiction.

Jupiter had graduated from Harvard with highest honors, without studying, and he was about to get a Ph.D. the same way. On the evening in question, Jupiter was on his way back to his dormitory room when he saw a light on in Professor Singer's study. He knocked, and when there was no answer, pushed the door open. The Professor was sitting in a chair, with his head resting on a desk. There was a beautifully wrought gold knife hilt sticking out of his coat, near the heart. The Professor was very dead.

The death of Harvard's expert on Italian Renaissance painting was the first high-class murder the Cambridge police force had had in years. Sergeant Rankin went to work with a will, and Jupiter joined the chase, but with his own methods. In the end, Jupiter's knowledge of painting, and his friendship for that pretty girl at the Fogg Museum turned up the solution of one of the liveliest mystery yarns in many a year.