It is just before Christmas and the marshal wants to go South to spend the holiday with his wife and family, but first he must recover from the flu (which has left the Florentine caribinieri short-handed) and also solve a murder. A seemingly respectable retired Englishman, living in a flat on the Via Maggio near the Santa Trinita bridge, was shot in the back during the night. He was well-connected and Scotland Yard has despatched two officers to "assist" the Italians in solving the crime. But it is the marshal, a quiet observer, not an intellectual, who manages to figure out what happened, and why.