December, 1916. Inspector Sam Blackstone is suspicious when he is called to the office of Superintendent Brigham - the new head of special branch - and confused that Brigham seems to want to see him as little as Sam himself wishes to be there. An already stranger situation grows more strange when Sam discovers what he's there for: a German traitor wants GBP25,000 in exchange for secret intelligence on U-boat locations, and 'Max' has specifically asked for Blackstone to be the one to deliver the money - alone. Blackstone, and his sergeant, Archie Patterson, are certain there's more to it than that, but Blackstone can't turn down the job - if he doesn't do it, some other poor fool will have to. But that is little comfort when, as suspected, it all goes wrong, and Blackstone finds himself on the run from his own colleagues, with Patterson languishing in a cell, looking at a twenty year stretch, if he's lucky . . . A chance meeting with a Russian former colleague seems to provide a lifeline, but his help comes at a cost . . .