We all know the feeling: you're alone but it's like there's someone there with you - a mysterious presence lurking just out of sight. Throughout history this experience has been the subject of religious and supernatural speculation. But does science have the answer? In Presence, psychologist Ben Alderson-Day digs into historical accounts and contemporary cases of 'felt presence', hunting for the key to unlock this strange phenomenon. He interviews ultrarunners and ocean rowers, who often report the sensation of being accompanied on their journeys, and examines the latest work on sleep paralysis, dementia and Parkinson's, conditions closely associated with feeling the presence of someone or something that isn't there. His findings, built on cutting-edge research from psychology and neuroscience, provide remarkable new insights into this longstanding mystery of the human mind.