Jennifer Marsh (Diane Lane) is a widowed single parent living in a suburban Portland home with her daughter Annie Haskins (Perla Haney-Jardine). By night, she works in the FBI's cybercrime division with Griffin Dowd (Colin Hanks), fighting identity theft and similar crimes. One night, an anonymous tip leads them to a website called killwithme.com. The site features a streaming video of a kitten being tortured and killed.
After the kitten's death, killwithme's webmaster (Joseph Cross) 'graduates' to human victims and makes their deaths correlate directly with the number of hits the site receives. At a press conference, the public is urged to avoid killwithme but, as Marsh feared, this only increases the site's popularity. The videos are recorded in the killer's basement and his various victims include a helicopter pilot (who is bled to death by injections of anticoagulant), a newscaster (burnt by heat lamps) and Dowd (killed by slowly increasing the concentration of sulfuric acid solution in which he is submerged).
At first it seems the victims were randomly chosen, but this is not the case. The first two victims were chosen because they were part of filming or presenting the suicide of a junior college teacher. The teacher's unstable, techno-prodigy son, Owen Reilly, broke down and was admitted to a psychiatric hospital. When released, he decided to prove a point (that the public is insatiable for the suffering of others), as well as wreak vengeance on those he felt had exploited his father's tragedy. Dowd was killed because he came close to the truth of who the murderer was. Marsh, who figures this out, is soon targeted as well.
Captured by Reilly, Marsh escapes her death-by-mulcher by swinging out of the way while dangling from the ceiling. She ends up breaking free and gunning down the murderer just as the other police show up, Marsh kills Reilly on his own website. As the film ends, the website receives numerous requests for a video of Reilly's death.