After Shawn, Gus, Lassiter and Juliet are decontaminated and cleared, they meet Dr. Reidman from the CDC at the hospital. Reidman tells them that only two people from the café are showing Thornburg symptoms. Luckily a lab only two hours away has been working on an antiviral for Thornburg, which is already on route to them. With the public health threat contained, Shawn and Gus talk to the victims, hoping they saw who left the vial at the café, but neither one of them noticed anything suspicious. As the guys are leaving, they see the antiviral arrive, and the lab it was shipped from is GenuTech. Shawn doesn't believe that's a coincidence, and he and Gus head to the lab. There, a lab tech tells them that he shipped all the antiviral to the hospital because they had underestimated the dose it would take to cure the virus, and unfortunately they can't make any more because their lab was shut down a week ago. He tells them Dr. Mallon, who was running the lab, lost funding, but now that there's an outbreak, they could be starting back up again. Shawn realizes that Mallon probably created the outbreak to justify further funding of his work. He looks through the personal effects Mallon left in the lab and finds a bus schedule, a theater program and a photo of him in front of a log cabin. Shawn recognizes Mallon as one of the victims in the hospital. They've got the culprit in quarantine. Shawn calls Juliet to warn her, but she tells them Mallon already broke out before he was treated with the antiviral. Shawn says he must have his own stash somewhere, but at least he doesn't have any more Thornburg to release. The lab tech overhears this and corrects Shawn – there are two more vials that are missing.
Back at the police station, the cops start up a manhunt for Mallon. Shawn remembers the bus schedule and the theater program and divines that Mallon will be at one of those two places. Dr. Reidman says the bus station makes the better target for a biological attack, and they all race down there to stop Mallon. They spot Mallon, who makes a break for it, losing one of the vials in the process. Shawn is able to recover the vial before it is compromised, but Mallon gets away. Shawn realizes that Mallon is sick because he didn't know he needed a bigger dose of the antiviral. He figures Mallon is headed back to the hospital for more, and he, Gus and Juliet are able to corner him there. Shawn offers to trade the cure for the last vial. Mallon agrees and hands over the cooler. As Juliet checks its contents, she cuts herself on the broken vial inside. Shawn turns back to Mallon for the last of the cure, but it's too late for both of them. Mallon says there is more antiviral but it's two hours away. He says the word “Victoria” and then dies.
Dr. Reidman puts Juliet into quarantine as Shawn, Gus and Lassiter try to decipher what Mallon meant by his last word. Shawn notices the GenuTech logo is a cabin, and remembers the picture in the lab. Shawn realizes that Victoria is the lake where Mallon's cabin is located. Lassiter says the lake is two hours away. Mallon must have the antiviral stashed at his cabin. Lassiter and Shawn race out as Gus stays with Juliet. At the cabin, Lassiter and Shawn are stymied by a raging Rottweiler. Shawn would do anything to save Juliet, so he puts on Lassiter's baseball catcher's gear and runs through the yard to distract the dog. Lassiter then dashes inside for the cure. They get back to the hospital in time, but Reidman tells them she doesn't need it. She was lucky and never contracted the virus. Shawn realizes it was too close a call, and goes to Juliet to finally tell her how he feels about her, but before he can finish, he is interrupted by Lassiter, who is ecstatic that is partner is going to be okay.