Doctor Benjamin Dalton has always been plagued by severe headaches, but given several recent strange occurrences concerning his Tampa, Florida, home and wife, those physical pains newly pale in comparison. Being a psychiatrist, he knows he should never let mere suspicion take over his life, but even with what little evidence he has, he's soon convinced that either something or someone purely evil is out to destroy both him and his family. Then the unthinkable happens and Anne Dalton becomes desperate to learn who or what her husband has become, and just who or what is sleeping in their bed.