Shawn, after a night in of drinking and listening to the chick-lit book series 'Internity' on audiotape, stops into a coffee shop with Gus before they are to be at a crime scene. Shawn, worse for wear, tells the barista that he will be getting his free since he will guess the trivia question again as always. However, he is beaten to the punch by Declan Rand, a handsome and charming man. Shawn wonders who he is as he leaves, but soon finds him across the street at their crime scene. Declan, it turns out, is a criminal profiler, brought onto the case by Chief Vick.
Shawn looks around the scene and sees an aerosol can. He then flashes back to crime scene photos of earlier cases we have not seen, and recalls similar cans at all of them. But before he can tell anyone about the link in the cases, Declan beats him to the punch.
Back at the police station, Declan delivers a profile of the killer to the police. He tells them the murders seem to be humane and are probably the work of a woman in her mid-thirties. Shawn then pulls Henry aside to protest Declan's hiring but Henry says competition will be good for Shawn. Shawn then tells Declan he doesn't believe he can get a psychological take on someone they don't know. Then Declan nails Shawn's personality spot on.
The coroner tells them all the victims suffered from different liver diseases. Then Shawn, remembering something from the doctors on 'Internity' concludes the victims were murdered for their placement on a liver donor list. They get the list from the hospital, proving Shawn's theory right. But the next person on the list who stands the most to gain is a woman in her mid-thirties, just as Declan said. Declan is also right and gets all the praise.
They track down Catherine and find out she's been out of town. The next two down on the list of suspects are also a bust. A witness to the first crime scene completes a sketch of the person who exchanged the aerosol can and it's Catherine. Shawn isn't convinced, and after he hears Declan quote 'Internity,' he realizes he's a fraud and now suspects him of the murders. Shawn and Gus confront Declan, who admits he's a fake but he didn't kill anyone. They believe him. The police say Catherine is now on the lam but they discover her dead in an office building with Declan over her body. They arrest him, but Shawn knows he's innocent. He figures out the truth, goes back to Catherine's apartment where he is not shocked to find Catherine's twin sister Maddy, the real killer.