Newspaper columnist John Klein (Gere) and his wife Mary (Messing) are involved in a car accident. Mary, the driver of the vehicle, swerves her car to avoid hitting something in the road. A brain scan reveals a tumor and she subsequently passes away. Later, John discovers an assortment of mysterious drawings which she created before her death, depicting a strange black winged creature she saw on the night of the accident.
Two years later, while driving to Richmond, Virginia, Klein gets lost and inexplicably finds himself far away in the small town of Point Pleasant, West Virginia. Klein's car breaks down, as he makes his way to a nearby house on foot to contact help. The owner of the house, Gordon Smallwood (Patton), reacts violently to Klein's appearance and holds him at gun point. Local police officer Connie Mills (Linney) defuses the situation while Smallwood explains that this is the third night in a row that Klein has knocked on his door asking to use a phone, much to the confusion of Klein. Klein ends up staying at a local motel and tries to figure out how he ended up lost from his original destination.
Officer Mills mentions to Klein that many strange things have been occurring in the past few weeks within Point Pleasant. While conversing with Smallwood one day, it is revealed to Klein that he had heard voices from his sink telling him that in Denver, 99 will die. Scared that Smallwood has the same ailment that contributed to his wife's death, Klein takes him to a doctor to get checked out. Smallwood is found to have a migraine, but no serious medical condition. While discussing the day's events at a local diner, Klein notices that the news is showing a story on an airplane crash in Denver that killed all 99 passengers aboard. The next night, Smallwood frantically explains that he had met the voices in his head. The being is named Indrid Cold.
Later that night, Smallwood calls Klein and says that he is standing with Indrid Cold. While Klein keeps Cold on the line, Officer Mills goes out to check on Smallwood. Cold answers Klein's questions, convincing him that he is a supernatural being. This episode starts a string of supernatural calls to Klein's motel room. One of these phone calls tells Klein that there will be a great tragedy on the Ohio River. Later, Klein receives a call from Smallwood and rushes to check on him. He finds Smallwood dead from exposure to the elements.
The entity described as the Mothman becomes a personal obsession for Klein. He meets an expert on the subject, Alexander Leek (Bates), who explains the nature of the supernatural being and details his own experience with it. As Klein reaches the bridge into town, there is traffic congestion originating from a malfunctioning traffic light. As Klein walks onto the bridge to investigate further, the bolts and supports of the bridge begin to strain at the weight. The bridge starts to come apart, making Klein realize that the tragedy that was prophesised to him was in fact the bridge. As the bridge collapes, Officer Mill's car falls into the water below. Klein jumps in after her and pulls her from the river and up to safety. As the two sit on the back of an ambulance, they see that they have just survived the collapse of the Silver Bridge. The epilogue displays a series of graphics stating that the cause of the bridge collapse was never fully determined. It also states that although the Mothman has been sighted in other parts of the world, it was never seen again in Point Pleasant.