In 1880 two twenty-year-old men, one French and one English, meet by chance while on holiday in Deauville. Jacques Rebière is the son of a former forester; Thomas Midwinter is descended from generations of landowners. Socially the pair therefore have little in common. But they instantly fall into friendship with each other because they share the same passion. Each wants to explore the mysterious and miraculous workings of the human brain and so to discover the causes of madness.