Sir Graham Forbes of Scotland Yard often calls upon Paul Temple to help with his latest unfathomable case...

Swinging between London and Geneva, Paul Temple and Steve are involved in a case that involves finding the answer to one vital question: is Carl Milbourne, thought to have perished in a car accident, still alive? There are those who are determined to stop the Temples discovering the truth. And Temple's own life is in danger.

Iris Archer agrees to appear in one of Paul Temple's plays, but then disappears until he sees her in a Scottish hotel when she is supposed to be in France. But how is this connected with a letter passed to Temple with a plea to deliver it to a Mr Richmond, and a network of spies with a shadowy leader called Z4?

Returning from America by ocean liner, the Temples meet wealthy Sam Portland whose UK agent Hubert Greene has received messages about Portland's past from a private detective called Madison. But Portland dies on board, and Temple is left to unravel a case involving international counterfeiters and the clue of a coin on a watch-chain.

On a boat trip from the fishing village of Downburgh, Paul and Steve Temple are shot at and later the boatman dies in a cliff-top fall. Back in London, the daughter of the head of M.I.5. has disappeared and it soon transpires there is a connection.

A series of eight murders, with in each case a card bearing the inscription "The Marquis", brings Temple into the hunt for a ruthless master criminal . Suspicion falls on an eminent Egyptologist, but there are other suspects and further murders before the Marquis is identified.