In this, the most personal of all his books, neurologist Oliver Sacks tells the story of an injury he sustained while climbing a mountain in Norway and the terrifying, bizarre aftermath when he realised with horror that his leg felt alienated. It did not feel like it was part of his body, but a foreign object somehow attached to him. This sort of disembodiment, with alterations in the mind-body image that affected Sacks deeply, was as confusing as it was frightening. When he finally recovered, he experienced unbounded joy and a new wonder for being properly "oriented" to his body.

With insight, learning, and an unusually unbuttoned metaphysical self-revelation in which he discusses his religious background and doubts, Sacks shows how the soul is stirred by the changes in the body.