When a murder occurs in a haunted house, it looks like the murderer might just be ... a ghost. On top of the investigation, Nick, Natalie, and Tracy all encounter ghosts from their own past after being in the house. When another man is apparently killed by the hand of the ghostly murderer, Nick and Tracy suspect their ghost may not be so dead. While they hunt for the murderer, all of them are haunted and must find a way to come to terms with their own ghosts.

A scientist is murdered and a lab rat escapes when industrial espionage goes awry. But far worse things begin to happen when the lab rat, infected with a newly engineered virus becomes Screed's next meal. Designed to combat HIV, the virus becomes lethal to vampires as it multiplies and intensifies each time they "feed". As the virus spreads rapidly through the vampire community, it infects Vachon, Nick, and LaCroix. Nick races agains time to find the killer - while Natalie struggles to find a cure.

An unusual murder leads Nick and Tracy to popular singer Christie Black, who is undergoing intense psychotherapy with the controversial Dr. Ben McGee. As more people close to Christie are killed, the suspects are dropping like flies. Nick needs to find the killer before there is no one left to kill. And apparently he'll have to do it without a partner as Tracy considers a transfer her father, Commissioner Vetter, has arranged.

A routine investigation into a suicide leads Nick and Tracy to an exorcist. As they witness an exorcism, Nick is overpowered by a terrible evil. Unable to control himself, Nick turns to LaCroix for help. But even LaCroix is powerless in the face of this evil, and at Nicks request, takes him to the exorcist to help free him from the Son of Belial.

A bullet wound to the head lands Nick in the emergency room, where with no pulse, no heart rate, and no brain activity, he is declared dead. Fast action by Natalie and LaCroix, brings Nick back to life. While his physical wounds are healing, his mind is another matter--he has amnesia, and therefore no memories of who he is or what he is. Both Natalie and LaCroix see this as a chance to acheive their goals for Nick. Who will win this little contest, and what will be the price? Meanwhile, Nick must find the killer before he strikes again, as well as find out who he really is.

An autopsy reveals a murdered woman's heart has been surgically removed, prompting Nick and Tracy to investigate the black market for human organs. Working undercover, Tracy visits a suspected dealer at the local hospital, unaware that Natalie Lambert is scheduled for a routine knee operation at the same facility. Upon learning Natalie has been chosen as the next "donor," Tracy is overcome by the dealer and prepped for the operation instead.

When Tracy is given a three-day leave after shooting a perpetrator, Nick works alone on a grisly murder investigation. However, Tracy ignores her orders and goes undercover at an escort service, putting her right in the sights of the killer. While Nick enlists the help of an infamous serial killer to try and find the killer, Tracy just might be the next victim.

A patron of the Raven is found dead, apparently killed by a vampire in unusual circumstances. The woman at the scene has no memory, and there are no clues. Nick must find the vampire-killer before he strikes again, while keeping Tracy out of trouble. For Tracy is aware it is a vampire, and is searching for the killer, too.

Both Natalie and Tracy start thinking about relationships, when a woman reveals on a talk show that her boyfriend is a vampire. When the woman is found murdered, Nick must find out if the murderer truly is a vampire and stop him before he strikes again. At the same time both Natalie and Tracy struggle with what to do about the relationships (or lack therof) with the men -- or rather vampires in their lives.

When a serial rapist is ripped to shreds by a dog, Natalie suspects that something isn't quite right. Nick's investigations leads him to suspect a carouche, a lower form of vampire who typically feeds on vermin, may be behind the dog's behavior. When Nick finds the dog, he discovers that it is the devoted companion of a blind dispatcher. Now he must figure out how to protect the dispatcher (and everybody else) from her not-so-mortal dog.

A man's death seems directly related to a court battle over Native American land. But when during the invesitigation Nick comes into contact with a spiritual healer who sees the darkness inside him, the case seems suddenly unimportant. As Nick focuses on the possibilities of this spirtual realm, strange things begin to happen. Things seem to go from bad to worse when the murders escalate, and Nick is afraid he may somehow be responsible.

When a grisly murder occurs, it complicates an undercover cop's investigation. Detective Bruce Spencer believes he knows who the murderer is, but since he has no proof, Nick is suspicious. It also doesn't help that Bruce and Tracy go way back and in Tracy's eyes he can do no wrong. When Nick witnesses Bruce's brutal behavior, he knows that nothing is as it seems, and he'd better find the murderer before he strikes again.

Nick's discovery that Tracy's mystery man, Vachon is a vampire, complicates an already complicated situation. Luckily Vachon and Tracy's mutal attraction saves Tracy's life. However, Tracy's awareness of vampires, and Vachon's penchant for running from his responsibilities place them all in danger as the bomber plots to use Tracy in his next bombing.

When an airplane transporting a bombing suspect and Schanke explodes, Nick becomes racked with guilt. He feels it should have been him on the plane and not Schanke. Nick turns in his badge, ready to move on to a new life. He decides to return when other police stations in the city start exploding.