Lassiter is having a drink after work at a bar when he meets a woman named Marlowe, to whom he is instantly attracted. He notices she is wearing a unique necklace. They hit it off immediately. After Lassiter tells her he is a cop, she asks to be excused to use the restroom. Several minutes pass by, and Lassiter thinks he has been stood up. Several minutes pass, and Lassiter checks the ladies restroom to see if Marlowe is okay. He doesn't find her. She has disappeared, and Lassiter is devastated.
The next morning, Lassiter arrives at a crime scene where a dead body is found. He gives special orders to McNab to find his mystery woman, Marlowe. They go to examine the body, and Shawn sees puncture wounds on the man's jugular vein and wrist. Lassiter is then devastated by the next clue he sees on the body - the same exact Eternal Life symbol necklace Marlowe was wearing at the bar. The woman he is infatuated with could be the person that murdered this man. Upon seeing the puncture wounds on the victim's wrist and neck, Shawn makes a bold proclamation that the killer was a vampire. And in a stunning turn of events, Lassiter jumps on board with Shawn's crazy theory and boldly agrees.
At the coroner Woody's office, Shawn, Gus, Lassiter and Juliet are told the body was drained of almost all its blood, thus causing the guys to further believe in their vampire theory. Juliet is the only person who isn't buying it.
Lassiter breaks off from Juliet. He heads to the jewelry store where the Eternal Life necklace was likely purchased and questions the store clerk. The store clerk says those necklaces are very popular and does not have a record of who would have purchased it. The clerk admires Lassiter's watch, causing Lassiter to take a closer look at it. In doing so, he sees a single fingerprint - Marlowe's fingerprint!
Juliet, Shawn, and Gus head to a vampire-themed bar to get the skinny on who might be the perpetrator of blood-thirsty murders. They meet a bartender who tells them he got a strange call from someone asking where they could get their hands on a pint of blood. Juliet, Shawn and Gus trace the number and are led to an address.
Meanwhile, Lassiter has found Marlowe. She has a solid alibi for the night of the murder. Also, Lassiter sees that she is still wearing her unique necklace -- an Eternal Life necklace -- thus, Lassiter knows it is not the same necklace as the one found in the dead grasp of the murder victim.
Shawn, Juliet, and Gus arrive at the house. They break in and find Lassiter with Marlowe. They are shocked to see this, but Lassiter quickly tells them that she is innocent. Upon further investigation of the apartment, they learn that Marlowe has three male roommates — one named Lucien. They question Lucien. Lucien explains that he was working at a miniature golf course at the time of the murder. Shawn notices a few things from the apartment... a cat litter box, a cracked mirror, and an address. Lucien tells them that those things are all in his roommate Ed's room. Ed is now a suspect. With that, they head straight to the address Shawn noticed at Marlowe home. They arrive the address and discover it is a blood bank.
At the blood bank, Shawn, Gus, and Juliet witness a series of strange occurrences that only further support Shawn's vampire theory. Then they see a cloaked figure break into the blood bank and flee the scene. They are unable to capture the suspect, but Shawn recognizes a jewel encrusted nail in the debris of the break-in and immediately Shawn makes the connection that Marlowe had the exact style of fingernails. She must have been behind the break-in. Shawn, Gus, and Juliet must get to Lassiter before Marlowe sucks him dry!
They arrive at Lassiter's apartment, and sure enough, Marlowe is there with him. Shawn presents the fingernail evidence, and Lassiter realizes he must arrest Marlowe as a murder suspect.
Later, at Marlowe's house, they find even more damning evidence - bags of blood she has stored and hidden. However, Marlowe's name is cleared from the murder when they get a call that another body has been drained of blood, but hasn't been declared dead yet. There's no way she could have done it because she was in police custody.
They all go to the hospital where Shawn makes the connection that all of the victims have the same blood type — O negative, an extremely rare blood type — and that only about a dozen people in Santa Barbara have it. Shawn discovers a name on the O negative blood list that tells him that Adrian Viccellio has the same last name as Marlowe, and that they must be related. Juliet then realizes a frightening piece of information - Lassiter has O negative type blood and therefore Adrian must be coming for his blood next.
Marlowe tries to warn Lassiter over the phone, but it's too late. Adrian lunges at Lassiter and covers Lassiter's mouth with a cloth drenched in chloroform. As Adrian sets up the equipment to drain Lassiter's blood, Lassiter comes to and Adrian tells him that he was a mark at the bar — that Marlowe was supposed to drug and drain him of his blood, but she didn't because she liked him. Lassiter manages to ovepower Adrian by himself just as Shawn, Juliet, and Gus show up to save Lassie. Lassiter tells the group that he was able to overpower Adrian because he has been building up a resistance to chloroform for the last 15 years. And with that, Adrian is taken into custody.
Later, Lassiter finds himself completely distraught about Marlowe being in jail. He visits her and tells her that despite her criminal activity, he knows that she was just trying to help her brother, and tells her that he will wait for her until she gets out.
- While the title goes for the pun on vampirism and blood-draining, the guest appearances by Tom Lenk (Andrew on the final seasons of Buffy the Vampire Slayer) and Corey Feldman (Edgar Frog in the classic vampire film The Lost Boys), as the bartender Thorn, bring two famous hunters of the fanged into the mix. There were several references to both scattered throughout the episode. Not the least of which is the guest star Kristy Swanson, who plays Marlowe. Swanson was the original "Buffy the Vampire Slayer" in the 1992 film which preceded the popular TV series of the same title.
- When Lassiter opens the door to Adrian, he asks Lassiter 'Is Tamara home?' a direct quote from the 2008 horror film The Strangers used when anyone would answer the door so The Strangers would know if someone was home.
- This episode reveals that Lassiter's mother is a lesbian. He struggled with this at first, but came to accept it.
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