As young boys both Jacques Rebière and Thomas Midwinter become fascinated with trying to understand the human mind. As psychiatrists, their quest takes them from the squalor of the Victorian lunatic asylum to the crowded lecture halls of the renowned Professor Charcot in Paris; from the heights of the Sierra Madre in California to the plains of unexplored Africa.
As the concerns of the old century fade and the First World War divides Europe, the two men's volatile relationship develops and changes, but is always tempered by one exceptional woman; Thomas's sister Sonia.
