"Once again John Boldre, head of the Modern History Department in the Cabinet Office is called on to investigate the why of a crime with political overtones while his police colleagues are co-operating in the discovery of who was responsible. But where they step gingerly from fact to fact, Boldre takes deductive leaps forward. His professional knowledge and store of useless information enables him to secure an investigatory foothold when a senior officer of Special Branch is murder on the top of a double-decker. The solution involves Boldre in a mental steeplechase over hurdles provided by an amateur operatic company, the Army, and French war-time resistence."