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.
Rosen and Bill stride purposefully through the halls of Alphas HQ, discussing a Red Flag prisoner that Cameron and Nina are apparently bringing in. "Good thing we got this thing up and running," Bill says, as the two reach a locked room that contains what is apparently a specialized Alpha holding cell, equipped with bulletproof glass, surge suppressors and fire-foam, as well as an emergency lockdown system. Let's hope those will be relevant to whatever still-unknown powers Cameron and Nina's prisoner possesses. Their expository conversation continues long enough for us to learn that Bill hasn't gotten his super-strength back since meeting Jonas, and Rosen says he's working on that; as glad as he is to have Bill around as an investigator, the DoD wants them to be a group of Alphas. Bill's still pointing out that Rosen isn't one (because we have to be reminded of that every week) when Gary comes in to bitch about all the Dr. Evil stuff the Alpha cell doesn't include. He also misses the old Bill, whose veins used to pop out (they really did), and also remarks on Bill's current ex-Alpha status. Bill really is a lot less tense, so much so that he's just amused by Gary these days. He even chuckles when Rachel comes in over the intercom acting like it's a police radio, reporting that Nina and Cameron are coming up in the elevator with one "Dr. Kern."
When the two of them arrive wheeling a clearly unconscious and restrained white-haired man in a cardigan, seated unconscious on a Hannibal Lecter hand truck, everyone's so keen to get him parked in the shiny new Alpha cell (because he's so scary, I guess) that nobody notices the elevator door's failure to close behind them...almost as if an invisible person blocked it, then followed them out. Rosen seems to sense something in the apparently empty hallway, but it's a little too late to make him an Alpha now.
After the credits, they're putting their still-unconscious prisoner into an MRI while Rosen's still trying to sell an uninterested Bill on bringing his powers back, but Bill insists he's happier without them. He certainly seems a lot more laid back, that's for sure. I bet he still touches other people's food, though.
Cameron and Nina are hanging out in her office while she updates the computer file on Kern. They discuss how quickly Kern got suspicious of their "happy couple" act, which allows Nina to tell Cameron that the possibility of a relationship between the two of them doesn't exactly have Rosen's seal of approval. She admits that Rosen thinks she'd be bad for Cameron, and doesn't entirely disagree. You can tell this is a serious conversation because Cameron's voice is shaking and Nina's not wearing makeup. Luckily, Bill calls them into a meeting before this can get much heavier. Less luckily, Nina leaves her computer unlocked with Dr. Kern's dossier up on the screen, and the invisible visitor starts scrolling through it. This is creepy -- whoever it was probably heard their whole personal conversation.