Sir Alec assigns Foyle to look into the case of a nervous spy, Karl Strasser, a former Nazi SS officer helping MI5 catch Russian agents. Strasser has been masquerading as a Dutch art professor teaching in London, but he has noticed someone following him. A bullet cartridge delivered to his room suggests he is on a hit list. Furthermore, his landlady and her lodgers appear to know his unsavory past.
As if this were not enough, the American embassy wants to extradite Strasser to the US to stand trial for the massacre of Allied prisoners in France during an operation called Sunflower. But MI5 stonewalls the US demand, since Strasser is too valuable to British intelligence. Fittingly, Strasser’s stalker leaves a sunflower on his bed.
Despite his distaste for the ex-Nazi, Foyle is strictly professional as he tries to get to the bottom of the anonymous threats. Things get nasty when Strasser takes a bullet on the street. It’s only a flesh wound, but the stalker has better luck when the hunted man is blown up by a powerful car bomb—which finally settles Strasser’s fate. Or does it?
Thanks to Sam’s legwork, Foyle tracks down the stalker, who turns out to be Thomas Nelson, a severely injured war veteran who recognized Strasser as the Nazi officer who ordered the massacre of Allied prisoners and then shot Nelson point-blank in the head during Operation Sunflower. Miraculously, Nelson survived. On spotting Strasser in London, Nelson followed him and planted the omens in his room. Later, he took a potshot at his tormentor.
But the car bombing was someone else’s work, namely MI5, which faked Strasser’s death to throw the US off his trail. The body in the bombed-out vehicle was not Strasser’s—as Foyle realized when he examined the corpse at the morgue, since there was no sign of the previous flesh wound. With the real Strasser on the verge of escaping from the country by air, American authorities show up at the remote air field and arrest him. At this point, the only loose end is Foyle’s future, since MI5 is annoyed with him and he with them.
In other action, life as a member of Parliament heads into cloak-and-dagger territory for Adam, as he investigates a suspicious reassessment of land engineered by his boss, Charles Roper, the Parliamentary Under-Secretary of State for Air. Unbeknownst to Adam, Sam gets involved by tapping the phone of the man who doubled the assessment on the property, making it impossible for the original owner to repurchase it after the war.
Adam confronts Roper with phone transcripts that implicate him. Claiming that he merely wanted to ensure that the land was used for agriculture, not development, Roper nonetheless resigns. Labour party leaders are furious with Adam for undermining one of their ministers. Adam is depressed that his parliamentary career is off to a bad start, but then he gets some good news: Sam is pregnant.