What does it take to fight in a modern war? Why did some men crack on the Western Front in the First World War and others endure? If 30 per cent of American troops fighting the Italians and Germans in North Africa became psychiatric casualties, what made the other 70 per cent (if they survived) different? Many of those who stayed and fought might have given the simple answer, 'courage'; but this begs in turn a question to which there is still no consensual answer: What is courage?

These issues are the very heart of Ben Shephard’s utterly absorbing study of the century-long relationship between psychiatry and the military. It has been an unhappy marriage; the two sides had a brief honeymoon, rowed, made up and rowed again. The real source of the discord is made clear in this remarkably rich and dramatic narrative: the army wanted men to be 'cured' quickly and returned to battle; the psychiatrists, all save the few sadists who agreed with the army, wanted to study neuroses in the raw and to find adequate therapeutic responses.

The starting point was shell shock. Shephard is at his best describing the bemused reaction of the authorities to tens of thousands of apparently fit young men manifesting debilitating gaits, tremors and tics, which rendered them quite incapable of further military service. Since the idea of a psychiatric