A Question of Possession by Justin Boote

When Amy encounters Greg naked, battered, and suffering amnesia in Fritton Woods, mumbling about 'lights', she is convinced he has been abducted by aliens, just like she was. Decided to help him, and at the same time prove the existence of extra-terrestrial entities, she takes him into her home while he recovers. But a series of strange incidents suggests to hospital psychiatrist Joan that Amy may have her diagnosis completely wrong. Maybe it's something far more terrifying; maybe he's been possessed by demons...