An officer, Eric, responds to a call of a woman screaming. When he gets there he sees a pimp trying to kill a prostitute. He kills the pimp, saving the woman. But after the ordeal, the Eric gets a call on his phone, and the man claims to be the pimp he just killed, saying, "You didn't think it would be that easy. It's not over."
They drive the prostitute home but Eric still wants to talk to her. He is curious about Rigo, the pimp that he killed but may have gotten a phone call from right after. She tells him that Rigo had no posse and no friends. Eric realizes that he knows the prostitute as his old friend's sister.
The memory of shooting Rigo keeps haunting his thoughts. He gets another call from Rigo on the phone, confusing Eric again, because he knows that he is dead. Rigo tells him that he's after Carla, the prostitute.
So Eric goes to talk to Carla again. He wants to protect her because he thinks Rigo is still after her. She refuses his offer of protection and he can do nothing else but leave her alone. Later that night, Angela, Eric's partner, calls him and tells him that Carla was found dead.
Upset over what has happened, Eric goes to visit a small vigil that has been set up for Carla. When he gets home that night, his phone starts to ring. He unplugs it from the wall, but it still rings. This time it isn't Rigo, it's Carla. She screams for help but Eric has no idea what to do. He doesn't know where she is and she gets attacked, presumably by Rigo, before she can tell him.
The next night we see Eric load up a gun and sit by the phone, waiting for it to ring. It does, but it's not Rigo or Carla. Its a man Eric asked to trace the calls for him. He tells Eric that they have been coming from a out-of-service pay phone in the same alley where he killed Rigo. He goes to the pay phone and yells for Rigo to answer. He tells Eric that he's right behind him. Eric leaves the pay phone and sees Rigo holding Carla with a knife to her throat like the first time he encountered them. Eric approaches Rigo and it looks like he stabs him. When they find his body, the man says it looks like a suicide - he was shot with his own gun.
At the end, Eric's partner Angela gets a call from Eric saying that everything is okay, and Carla's safe now, because he is there to protect her.