Oxford, 1942. Frederick Rowlands receives an urgent summons to the university city from his old friend - also a blinded war veteran - Major Ian Fraser. They are to meet Professor Duncan Challoner, Fellow of Brasenose College, now working with MI5 at nearby Blenheim Palace. Challoner is about to divulge the identity of an enemy agent at Blenheim - but is murdered before he can do so. Also taking an interest in the case is MI5 agent Iris Barnes, who has her own reasons for wanting to track down the traitor.

Now the race is on to find the murderer before he - or she - can kill again, and to prevent vital plans for a covert British mission to steal key components of the German radar system from under the enemy's nose being compromised. For Rowlands, the stakes could not be higher, in this deadly game of cat-and-mouse.