For years, Oliver Sacks is the explorer and magnificent chronicler of a rare planet of uncertain borders. A universe populated by people to whom an accident or disease have confined in the difficult territories of madness, difference, strangeness. Of noteable subtlety as a writer, a poet of the stature of William Auden called Migrafia, his first book, "masterpiece", Sacks is also a penetrating researcher, endowed with a special sensitivity to listen to the patient, to shed light on ourselves And our "normality" by observing very "normal" areas. And so, entering the very curious "clinical cases" that support his work is always for the reader a wonderful journey of discovery. On this occasion, his gaze is directed at himself for the first time, and he is his own patient. After an accident in a desolate mountain of Norway, suffers a wound in a leg, serious but not unusual. But then, during what should be a routine recovery period, he begins to experience the overwhelming feeling that the leg has become a part of his body alien to him, which no longer belongs to him. And this disturbing experience will be the starting point of a fascinating journey through the mysteries of the perception of the body itself, the physical substratum of our identity, the horrors and wonders that are usually hidden behind the surface of health.