As a child, Dr Alice Arnolds witnessed the death of her brother while she was sleepwalking. She has devoted her professional life to unravelling the secrets of various conditions that impact patients while they sleep. She is drawn to Charlie Morgan and his wife Sarah, whose family has been torn apart by things that go bump in the night. The couple have lost one child and their remaining offspring, Emily and Daniel, are also in peril. Daniel is particularly susceptible to sleep paralysis.