Dr. John Watson is back home, recovering from his time in the trenches of Flanders Fields. The horrors of war weigh heavy on his mind, and now his task is to help rehabilitate soldiers suffering from the crippling effects of shellshock.

But the war is not yet over and in one corner of England lies a secret, one that the establishment is determined to keep under wraps. For in the woodlands of the lush countryside, the government is building the secret weapon which will win the war for Britain. Here, they are developing the never-before-seen tanks which the army is convinced will end the stalemate on the Western Front.

But then disaster strikes. After a training exercise in one of the tanks, eight men are mysteriously struck down, seven of them dead. There is just the one survivor, and he's not talking. It is clear something is horribly wrong, and the army calls in the only man who will know how to solve the mystery: Dr John Watson.