Taking the codebook from the petty officer’s kitbag, one night in 1944, in the little Wolverton pub, had been like tossing a stone into the ocean. The ripples of it seemed endless. Now, some sixty years later, time finally catches up with Bletchley Park veteran Elsie Sidthorpe, as she is tested once again by Günther Möller, the renegade German with his own hidden past. This time Elsie has an insurance policy. Or two, in fact. When the first of them fails, Bletchley Park curator Harry Stammers is thrust into a desperate race to unravel their secrets and the truth about a mother who has been missing since his childhood.
With the mysterious ‘Smith’ manipulating events for his own covert ends and Möller preparing his final move, Stammers and the acid-tongued Jane Mears must accomplish the impossible. But not before they have deciphered the secrets of BUILDING 41.