The main character, Sarah, is a successful single woman who has always believed that she didn't need a man to have a family. However, after undergoing a fertility treatment, she finds out that she has become pregnant and decides to keep the baby.
One day, while out for a walk, Sarah is attacked by a stranger and is saved by a man named Jake. Grateful for his help, Sarah strikes up a friendship with Jake and the two become close.
As Sarah's pregnancy progresses, she begins to notice strange behavior from Jake. He seems overly interested in her and her unborn child, and she starts to suspect that he may have ulterior motives for befriending her.
It is eventually revealed that Jake is the anonymous sperm donor who fathered Sarah's baby, as well as several others. He has been keeping tabs on all of the children he sired and has even gone so far as to try to rekindle relationships with their mothers.
When Sarah finds out the truth about Jake, she becomes terrified for the safety of her child. She works with the police to try and stop him before he can do any harm.
The film ends with a dramatic showdown between Sarah and Jake, and Sarah ultimately triumphs, saving both herself and her baby from Jake's dangerous obsession.