An Arctic installation. A man, running its halls, frantic and afraid. Pursued by two eerily calm men in white hazard suits. They track and find him, and one offers him some water. When it's swallowed, the frightened man's throat starts convulsing in an unnatural way. It's creepy.
After that little bit of WTF-ery, we cut to the Centers for Disease Control in Atlanta. Handsome and charming CDC field operative Dr. Alan Farragut is busy being handsome and charming in front of a class of new minions, making them think he almost killed them with cholera when, in fact, the test tube he flung across the room was filled with Scotch. His show is interrupted by the appearance of his ex-wife, Dr. Julia Walker, also a CDC high muckety-muck, accompanied by Army man Major Sergio Balleseros. They've got an emergency: An outbreak at a privately run Arctic research base. Why should (name) care? One of the patients - that guy we saw at the beginning - is his brother, Peter.
Dun dun dun! We're off to the Arctic. The team - Alan, Julia, and Balleseros are joined by Farragut's minions, Dr. Sarah Jordan and Doctor Doreen Boyle. They're met at the entrance to the facility by its head, Dr. Hiroshi Hatake, and his head of security, Daniel Aerov. The team gets the download - Peter's not well, the virus isn't airborne, and since the low temperatures mess with helicopters, there's no easy way off the base, and said base is pretty damn big.
First things first: Drs. Farragut and Walker suit up to go see Peter. The tension is palpable, since what broke up the marriage was a tryst between Dr. Walker and Peter. But these guys are pros, so they're in to check out the patient. Peter's in bad shape; pale, vitals all over the place, black lines running down his neck. But when the examination starts, Peter freaks out and attempts to attack his brother with a syringe filled with his own black blood. Only quick action by Dr. Walker allows him to be sedated in time. Things go only slightly more smoothly when they investigate the other patients, as an open body bag reveals a disintegrated corpse, leading Dr. Jordan to expel her lunch all over in the inside of her hazard suit.
Meanwhile, Dr. Boyle and Major Balleseros are investigating Peter's lab under Aerov's watchful eye. The security chief confounds our investigators with his claim that the base has no monkeys. Dr. Boyle puts the lie to that claim by discovering some hair from a rhesus, and the mystery deepens - why the simian skullduggery?
In another part of the facility, Alan makes another strange find - Peter left a secret signal, one the two used to use as kids to warn each other about their alcoholic father, in a video diary. So, he knew something was up. But what, exactly?
Alan won't get to ask, because he's quickly summoned to the room where Peter is being held...or, *was* being held, as he apparently tore a hole in the ceiling and escaped. Aerov's solution is to flood the air ducts with gas, and it's done over Alan's objection. A tense hunt through the tubes, though, turns up not Peter, but the body of a murdered scientist...well, most of it, anyway. It seems Peter took the victim's left hand with him.
At the same time, Boyle and Balleseros have a tense moment of their own tracking down what seems to be the lab's last monkey. It dies after attacking Boyle, but she's lucky - her skin wasn't broken. And what's more, the monkey is showing throat vibrations like those that struck Peter at the beginning of the episode.
And things just keep getting weirder. We see Balleseros planting some sort of device outside before he happens on a field of frozen monkeys, followed by a tense conversation with Hatake in which it's revealed they're working for the same people. And Drs. Jordan and Walker use the electron microscope to figure out that our deadly virus is a mutagen that appears to be "changing" Peter. We're left with Alan's question: "Into what?"