What's a twenty-two-year-old Irish cop from Boston doing at Beardsley Hall having lunch with Haakon, King of Norway, and the rest of the Norwegian government in exile? Billy Boyle himself wonders. Back home, he'd just made detective (with a little help from family and friends) when war was declared. Unwilling to fight-and perhaps die-for England, he was relieved when his mother wangled a job for him on the staff of a general married to her distant cousin, Mamie. But the general turns out to be Dwight D. Eisenhower; his headquarters are in London, which is undergoing the Blitz; and Uncle Ike has a special assignment for Billy: He wants Billy to be his personal investigator.

Operation Jupiter, the impending invasion of Norway, is being planned. Billy is to catch a spy amongst the Norwegians. He doubts his own abilities, and a theft and two murders test his investigative powers. But to his own surprise, Billy proves to be a better detective than anyone suspected.