"A German defector, the enigmatic Sigrid Lang, has conferred slivers of information to British spies embedded in Pforzheim: whispers of the secret weapon known as Erdschlag. Sam must bring her to safety before she will give up all that she knows. Fearing that the massive tank is near completion, Sigrid has warned those who can aid her that it will soon leave its home and point its barrel at London. And capable of blowing Sam's cover at any moment is Lothar Eichler, bested by Sam during their first rendezvous and now seeing saboteurs in every face. The fearsome man will stop at nothing to ensure his project elevates his stature in the regime."