A DI Hardcastle Investigation - June 1917. Ernest Hardcastle, head of the Whitehall CID, is called to investigate the murder of Sir Nigel Strang, permanent secretary at the Ministry of Munitions, in his office. Given his work, Hardcastle wonders whether the Germans might be responsible. Then another murder leads Hardcastle to a worker at Woolwich Arsenal, who is suspected of passing information to the enemy. But is there a connection? Hardcastle must find out . . .