Sergeant Verity's adversaries in the underworld are as busy as ever, this time taking advantage of the Brighton Races to dupe the populace, and, more seriously, to steal the beautiful Shah Jehan clasp. Everyone knows that the glistening jewel is priceless, but only the likes of Sealskin Kite and Old Mole know its true worth.

Down from Paddington Green with his family and his old accomplice Miss Jolly, Verity thinks he has crime at bay in Brighton. But the easy time he had anticipated soon turns into a nightmare of false alarms, public disgrace and, worst of all, personal disaster.