Yugoslavia before Marshal Tito’s break with Russia. In a cafe facing the harbour of Dubrovnik two Englishmen are sitting, watched by Zarko, the Chief of Police. 

Robert Hudson, an engineer, has known John Raikes for only three weeks—Raikes has been introduced to him as a technical consultant from the British Board of Trade, and the two of them are completing negotiations for the supply of certain machinery to the Yugoslav Government. 

Within a few hours Raikes is reported dead—“a tragic accident while bathing,” says Zarko. Hudson, alone in an atmosphere of ill-concealed hostility, determines to fulfil a mission of which he himself has only a hazy knowledge.