The year is 1793 and Herbert Powyss is set on making his name as a scientist. Determined to study the effects of prolonged solitude on another human being, he advertises for someone willing to live in his cellar for seven years in return for a generous financial reward. The only man to apply is John Warlow, a semi-literate farm labourer with a wife and six children to support. Cut off from nature, Warlow soon begins losing his grip on sanity while, above ground, Powyss rapidly becomes obsessed with Warlow’s wife, Hannah.