American computer whiz Luke Williams meets elderly Lavinia Fullerton on a London-bound train. She reveals she's discovered the identity of a serial killer in her village and is going to report it to Scotland Yard. When she is murdered after disembarking the train, Williams vows to pursue the case himself.

While working in a diamond mine located in the desert, Bo and Ingrid, two siblings who survived a massacre as children, make a surprising discovery.

Inspector Clouseau disappears, and the Surete wants the world's second best detective to look for him. However, Clouseau's enemy, Dreyfus, rigs the Surete's computer to select, instead, the world's WORST detective, NYPD Sgt. Clifton Sleigh. Sleigh obtusely bungles his way past assassins and corrupt officials as though he were Clouseau's American cousin.