In the opening scene, a young girl feasts on the blood of a dead lamb.
Back from a business trip, lawyer Tom Martin meets his wife, Sarah, at the airport. After a change of clothes, they drive to Harry's cottage in Somerset, for a short holiday.
Driving to the destination, Tom loses control of the car and is sent on an out-of-control spin at 100mph. Eventually, he takes control of the car and pulls into a cutaway.
They walk through the woods to look for help and discover an old house. Mrs Ardoy lives in the house with her huge brood of children, and she offers the couple a room for the night.
At night, Tom walks through the woods to get the luggage from his car. Sarah follows him and meets him running for his life from a strange creature. Eventually, they make it back to the house.
After being shown to their room by Mrs Ardoy, Sarah is sure that she saw something at the window. Tom finds that the door has been locked, so he climbs down the drainpipe to investigate and manages to fall. Sarah, meanwhile, is attacked in the room by a creature.
When Tom wakes up, he finds himself in a hospital bed. Sarah tells him that they had a bad car accident and that he has been unconscious ever since. Tom tells her of the strange Mrs Ardoy, but Sarah simply explains that he must have dreamt it all.
When Tom leaves hospital, he notices that his wife is acting very oddly. She begins to eat raw meat, and Tom confides to his work colleague that she has an increased appetite for sex. Sarah also breaks the news to Tom that she has fallen pregnant. According to the doctor, the foetus is growing at an incredible rate.
One day, when Tom comes home from work, he finds no sign of his wife. Her bags have gone. Tom knows instantly where she has gone.
When Sarah arrives at the Ardoys she is greeted by the children and they help to hide her car. Sarah is told that she was expected and taken to a room in preparation for childbirth.
When Tom arrives he parks his car and starts walking through the woods. He meets an axe wielding woodsman and asks him if he knows of a house and large family who live nearby. The woodsman denies any knowledge. With the night drawing in, the woodsman's appearance begins to change. He raises his axe and brings it down on Tom.
Meanwhile, Sarah has given birth. She has died during childbirth and now Mrs Ardoy has another child to raise.