I read this in one sitting, and knew immediately it was one of those series of which I had to buy the next book even if it meant going without cigarettes for a while.
The haunted Ian Rutledge, a former officer who served in the muddy of trenches of World World I, and Hamish, the young soldier he was forced to shoot for insubordination after he refuses to lead more men above the ridge and into the slaughter, are such complex characters that their internal struggles (if Hamish can be said to have internal struggles anymore) are as riveting as the beautifully executed mystery.
The war is over, but Rutledge, released from the mental institution, returns to his job as a Scottland Yard inspector a haunted man--literally. He is dogged by the relentless hallucination of Hamish, always present, always following him, muttering disdainfully in Ian's ear. Ian knows Hamish is dead, that it is merely a reflection of his shattered mental health, but the hallucination is too vivid too ignore. So Ian struggles to drown Hamish out, to not answer him aloud, and--most importantly for the context of the time--to appear sane. His supervisor already despises Rutledge, so it won't take much of a slip up to end up fired, only increasing the pressure on Rutledge's pained and restless mind.
Post-WWI-England is vividly portrayed with little (but well-researched and well-placed) details. Passing comments made by the characters in this series often linger for quite some time. Absorbing both for the characters and the mystery (with wonderfully classic--yet not cliche--touches), this series is one of those that will have many readers waiting impatiently for the next installment.