A subway car full of commuters suddenly seems overtaken by some kind of Rage virus, and Dr. Rosen and the team are brought in to figure out if an Alpha was behind it and other recent riots. After Rachel ascertains that the car was redolent with pheromones that trigger aggressive behavior, it sure looks like that's the case. They soon track down a young woman who seems to have been the epicenter, but in trying to nab her, they instead get their hands on a young man who was also there. He claims to be the girl's brother Matthew, the only one who can control her, although he clearly sucks at it. Rosen has just about convinced the kid to help them find his sister when Don Wilson (a returning Callum Keith Rennie) shows up and gets all pissy, just as the team realizes that Matthew's lying. Which not only blows the whole deal, but leads to the reveal that Matthew is the one who's been triggering the pheromone-fueled riots. Which he forthwith does, right there in Alpha HQ, with the unfortunate result that Callum Keith Rennie suffers yet another violent death on the SyFy channel, although it's at least as a different character this time.
So Matthew's on the loose again, but at least Rosen's figured out that Bill was immune to Matthew's pheromones thanks to his high serotonin level, which allows Rosen to inoculate him and Cameron before sending them out to catch Matthew again. Turns out the girl is just his ex-girlfriend who's been on the run from his creepy stalker ass, and although he starts not one but two rage-riots at the bus station, Cameron saves the girl and Bill catches the bad guy. Who ends up at Binghamton under Agent Cley's not-so-tender mercies, while the team talks some more about its tenuous future. I think I'll probably understand the show's premise better if it just explains it to me a few dozen more times.