Four months before Christmas, Sarah and Matthieu Scarangelo were in a car crash, of which Sarah and her unborn baby were the only survivors. On Christmas Eve, Sarah stays home alone, where she grieves her husband and prepares to go to the hospital the next morning for the delivery. As night falls, a woman knocks on Sarah's door asking to use the phone. When she refuses, the woman reveals that she knows Sarah and tries to force her way in. Sarah calls the police; they inspect the home and determine the woman has left, but promise to keep watch over Sarah through the night. The woman returns and tries to take Sarah's unborn child, but Sarah locks herself in the bathroom. The strange woman torments Sarah through the night and kills all who try help her.

John Klein is involved in a car accident with his wife, but while he is unharmed, his wife mentions a moth shaped creature appearing. After her death, John begins to investigate the secrets behind this mentioned Mothman. It takes him to a small town of Point Pleasant, West Virginia, where he discovers a connection with the same problem. Here he meets Connie Mills, while he continues to unravel the mystery of what the Mothman really is.

In England, retired marine Harry Brown spends his lonely life between the hospital, where his beloved wife Kath is terminally ill, and playing chess with his only friend Leonard Attwell in the Barge pub owned by Sid Rourke. After the death of Kath, Len tells his grieving friend that the local gang is harassing him and he is carrying an old bayonet for self-defense; the widower suggests him to go to the police. When Len is beaten, then stabbed to death in an underground passage, Inspector Alice Frampton and her partner Sergeant Terry Hicock are sent to investigate. They pay Harry a visit but don't have good news; the police have not found any other evidence, other than the bayonet, in order to arrest the hoodlums. This mean that should the case go to trial the gang would claim self-defense. Harry Brown sees that justice will not be granted and decides to take matters into his own hands.