A Test of Wills — Charles Todd

It's 1919, and the War to End All Wars has been won. But for Scotland Yard Inspector Ian Rutledge, recently returned from the battlefields of France, there is no peace. Suffering from shell shock, tormented by the mocking, ever-present voice of the young Scot he had executed for refusing to fight, Rutledge plunges into his work to save his sanity. But his first assignment is a case certain to spell disaster, personally and professionally.

In Warwickshire, a popular colonel has been murdered, and the main suspect is a decorated war hero and close friend of the Prince of Wales. The case is a political minefield, and no matter what the outcome, Rutledge may not escape with his career intact. But, win or lose, the cost could be even higher: the one witness who could break the case is himself a shell shock victim, teetering on the edge of reality. And in this war-ravaged man, Rutledge sees his own possible future, should he lose grip on his mind....