Psych: Season 4, Episode 13

4 - 13: Death Is in the Air

A courier named Donny Lieberman (Ernie Grunwald) loses a cooler containing the deadly Thornburg virus, so he asks Shawn and Gus to help him find it, and Shawn realizes that the same lab that Donny was working for is somehow involved. Luckily, they get help from Dr. Steven Reidman (Judd Nelson), the foremost expert on the virus who also expresses interest towards Santa Barbara's favorite psychic. In the race to stop an outbreak, Shawn has an epiphany concerning Juliet.