Romain is a "moon child", afflicted since birth by a rare genetic deficiency that makes him unable to stand exposure to daylight. Since infancy he has been cared for by David, a consultant dermatologist  who is fascinated with his case  and with whom he has developed an unusually close relationship. Now David has to leave, and doesn't know how to tell Romain.

The day of the separation draws near... a new ordeal for them both.