"I'm taking what's mine."
Dennis Quinn is the nerdy and insecure friend of Marty Jackson who Jackson introduces to his mother Meg Morrissoon afterwards she starts getting mysterious phone calls by a threatening person, when Quinn learns of this at the same time Marty does he takes on the idea and begins to harass Meg with the same phone calls.
They get so bad that she soon involves the police and they place her under police protection.
In the end it turns out to be Quinn who has called and also murdered at least two other people (a prostitute and a policeman, in which he called Meg when the police where there and he was murdering a woman in the process).
Dennis attacks Meg at home under knife-point. She is rescued by the police and Dennis is arrested.