When a meek mom of a teenage girl calls the wrong number, she finds her life in jeopardy when the unbalanced recipient loses everything because of her mistake and seeks the ultimate revenge.

Nicole Williams has lost closeness with her teen daughter Katie after divorcing her dad. While watching Katie one night, her daughter becomes ill and Nicole calls the school in the wee morning hours to let them know she won't be coming in, only she dials the wrong number. The call wakes Matt Hoffman. When no one leaves a message, Matt dials the number to find out who had called. Nicole is too worried to answer. The next day, she forgets about the incident and goes on with her life.

Only Matt isn't quite able to do so. At his job, he had a big presentation the next day, crucial for his company to succeed. After Nicole's accidental call, Matt is unable to go back to sleep and finds himself sleep deprived at work. The presentation that he has prepared so long for goes awry, to the point that his company loses a big contract and he finds himself fired. Too ashamed to tell his live-in girlfriend Samantha, Matt pretends everything is normal but in reality, rage stews inside him against the caller who had woken him at an ungodly hour.

Without the income and being denied unemployment, Matt's life crumbles even worse. His new car is repossessed. Bills aren't being paid. His house could be foreclosed on. Once things escalate, Samantha realizes what has happened and offers to assist him financially. A man of pride, Matt refuses to accept, and even alienates his girlfriend to the point of her moving out.

While Matt sinks further into psychosis, he begins calling Nicole and not saying anything. The calls become obsessive so Nicole blocks his number. Matt won't have it. He gets a new number and continues the calls. Also tracks down Nicole's address and information about her.

Nicole has an uneasy feeling about her silent caller and takes precautions to ward off any unwanted surprises. Katie feels her mom is too much of a pushover and tells Matt off the next time he calls her mom's cell. Instead of achieving the desired result of making the lunatic stop calling, her verbal assault has the opposite effect - it makes Matt so angry that he loses his sanity and decides to act.

Matt takes Nicole and Katie prisoner in their own home and makes light of their situation as he contemplates how to kill them. Nicole must reach deep inside her to find an inner strength she never knew she had in order to stop their stalker before it's too late.