Cameron and Nina bring in a Red Flag suspect named Dr. Kern, who is quickly installed in the new anti-Alpha holding cell. We soon learn three things about him: he’s got no optic nerve and “sees” his surroundings by using a form of sonar; he’s an obstetrician who’s been distributing mutation-promoting vitamins; and he’s played by Brent Spiner. What seems more immediately urgent, however, is that there appears to be an invisible invader walking freely around Alpha HQ.
Soon Rachel is also invisible, as in missing, and with Kern’s help they realize there’s another Alpha in the mix, an assassin who’s after him. His claim is that they’ll only be able to survive if he helps them out, but rather than cutting him loose, they figure out a way to flush out the invader on their own, using Gary and cameras and a giant mess. But not without Cameron taking an invisible knife to the gut. So the good news is that the formerly invisible assassin, Griffin, is soon locked down, but she warns them that all the cracks that have been suddenly appearing around the office are the work of Kern, who is using his sonic abilities to shake the whole building down around them.
Sure enough, Kern is able to blast right out of the cell using sonic waves, incapacitating the team long enough to get to Griffin. Luckily for her, Bill recovers (and his powers, absent since tangling with Jonas last episode, also return) in time to distract Kern — allowing Griffin to kill Kern and make her escape. Before leaving, she gives Bill the clue “Stanton Parish,” whatever that means. She also got away with all the goods on what Kern was up to OB-wise, so all that’s left for the team to do is try to clean up their trashed office and feel stupid about having tried to hold an Alpha there in the first place. Also, it looks like Cameron has finally convinced Nina to date him, against Rosen’s advice, if anyone cares.