The book tells true stories of survival in monotonous environments. The mind sometimes conjures up a presence (this sensation can also be invoked by brain stimulation) which feels like a "guardian angel" or imagined person who remains just out of sight and gives good advice and disappears when no longer needed. Geiger talks about accounts through the ages and in modern times: polar explorers, pilots, divers, mountain climbers, etc. He explains the phenomenon in biological rather than mystical terms. The bood was fascinating but the accounts are all somewhat the same, so you can skip to the end of the book for a plausible explanation. ( )