A bike courier gets on an elevator with a guy who's very sweaty and has a nosebleed. They get off on the same floor, of what appears to be an oil company. The man collapses and appears to die, only to start spewing a red mist all over the concerned office inhabitants.
The mist is blood, sprayed out by the man's rupturing veins. Then the bike courier gets a telltale nosebleed, and he attempts to get out of the building by dies in the same painful way before he can get out. Walter makes the snap decision to quarantine the building, which traps Olivia and Peter inside.
So everyone but Olivia and Peter have died gruesome deaths, and Peter slips in some blood and is likely infected too, but everyone knows incubation rates are much slower for people whose names come first in the credits. A little detective work determines the man who died first was there to sell something to the oil company, and a briefcase found in the man's rental car contains a sample of the virus found in a geological sample.
Walter, butting heads with the suits at the CDC (who are preparing a "level 6 eradication" for the building), figures the virus is an ancient disease that wiped out mammals in the ice age, and the virus has enough of a personality that it wants to get out of the building, meaning the infected turn into rageaholics trying to smash their way out so the virus can wipe out the planet, oh, let's say 28 weeks later.
And yep, Peter's infected, but he manages to foil the tox screen prepared by his dad, and is almost out of the building before a nosebleed gives him away. Peter mad! Peter smash!
Walter, having gone inside to do the tox screen and not wanting to leave his son, manages to MacGyver up a sample of an antidote from the company's break room fridge, but the nearest chemical procurement facility or whatever that could make enough is too far away for the CDC's exterminator, and he's ready to send in the troops. Broyles and Olivia try to buy time by pumping a sedative through the building's ventilation system, but it was turned off to prevent the pathogen from escaping, so Olivia's got to head back inside to turn it on.
Inside, she's attacked by a fury-blinded Peter, who beats on her, grabs her gun and heads up the elevator so he can shoot his way out (not that he'd make it with the firepower the Army's bringing). But Olivia manages to get the ventilation system turned out, the gas is pumped in, everyone goes night-night for a while, giving Walter enough time to cure them.
And this should be noted: during the crisis, Walter, upset over Peter being infected, says, "I can't let Peter die again." Later, Astrid asks him what he meant. He tells her to mind her own beeswax.
Into the elevator he goes, which already holds an older man with close-cropped hair, who's already pushed the button for the 16th floor, which is where the courier's going. "Going to be a nice one today," says the courier as he glances over the man, receiving a curt agreement in accented English from the other dude. There's a little bit of sweat rolling down the older man's face. "You don't look so good," says the courier, which is easy for him to say, with his youth and his hairline! The older guy turns his head, and there's a little trickle of blood coming from his left nostril. He wipes his nose with a tissue, but there's more blood coming, and as they get off the elevator, he's pale and glistening with sweat. He wanders away from the direction of Vitas Petrol's reception desk, and the courier tells "Helen" that he thinks there's something wrong with the guy. Helen calls to him to tell him he needs to sign in, and the older guy looks at her, and it's not clear if he's even comprehending her.
Then he collapses and is on his back on the floor while people freak out and the courier performs CPR on the guy to no avail. He checks for a pulse around the guy's neck. "He's dead," the courier tells the office worker who was trying to help.
But wait, there's more! Suddenly the veins in the dead guy's body are all standing out in sharp relief as his body convulses, and a red mist spews from the corpse's mouth, splattering on everybody nearby, which is a lot of people, since the looky-loos had all come over to see what was going on. In a talking head, Michael Scott says, "Reminds me of the time Meredith collapsed after a bender the night before."
After the opening credits, we watch Astrid anxiously make her way through the Boston Children's Science Center, until she's stopped by a helpful employee. Astrid says she's looking for someone who's lost, and the employee assumes she's talking about a kid, but it doesn't take a genius to see where this is going. "Ah. A special needs individual," says the employee when Astrid tells him it's not a student but a man. "You have no idea," says Astrid.
Sure enough, there's Walter, lecturing a bunch of kids about the history of the first circumnavigation of the world, and that when the Victoria arrived back home, only eighteen of the original 237 crew members were on board. A little girl asks what happened to everyone. "They all died, little girl, horrible and most likely painful deaths," says Walter, looking slightly annoyed at being asked, while the woman with the "Science is fun!" sticker on her sweater looks uncomfortable. Heh. Walter starts telling them about the price to pay for opening certain doors, and gives them the example of how when you check under your beds for monsters, you are immediately eaten, whereas if you hadn't looked, you wouldn't wind up "being slowly digested in the stomach-sac of the creature." I'm not convinced this is as self-evident as he seems to think it is. The bright side, though, is that maybe their screams will serve as stark reminders of the grim butcheries that await us under our beds.
Aaaaaand Walter's got his season pass revoked, and he's not happy about it. He mutters as he and Astrid leave the centre, Astrid pointing out that he terrified the kids. "These children should know the truth. They're tragically coddled and ill-advised," he grumbles. And while he attempts to cause the children to burst into flames on the strength of his withering glare, Astrid takes a phone call from Olivia, and tells Agent Dunham they'll be there right away.
Peter and Olivia are already at Vitas Petrol, taking in the scene. A body under a yellow tarp on one side of the office, a bunch of nervous office workers congregated on the other side. A detective Kassel welcomes them, saying they're taking witness statements, and hands over the dead guy's Dutch driver's licence: Poor Radjan VandenKemp. They pull back the tarp and have a look at the blood and Radjan's blood-drained face. "I've never seen anything like this," says the detective, which lets Peter give him a been-there-done-that "lucky you."
Olivia goes off to talk to the witnesses, and asks the receptionist if the guy had an appointment there, and she says no: "No one knew him. No one was expecting him," she says, adding that when he got off the elevator, he seemed confused, and then he collapsed.
Peter gets off the phone with Broyles, who's downstairs, and tells Olivia that Broyles is going to run VandenKemp's name and see what turns up.
Up strolls Vincent Ames, who introduces himself as the VP of geotechnical engineering. And Olivia without her camera! He asks if they're going to be able to leave soon, and Olivia says not yet. Vincent glances at the tarp-covered body and aks if they know what happened to him yet. "That's what we're trying to figure out. But we'll let you know as soon as you can leave," she says.
The receptionist tells Olivia that courier Mike rode up with him. Which one's Mike, Olivia wants to know, and the receptionist points out the guy who looks ready to shit his pants any minute -- only he's gone.
He's in the bathroom, splashing water on his face ... and then droplets of blood in the sink make him look in the mirror and see the trickle of blood running from his nostril.
Outside, Broyles strolls over to Astrid and Walter and tells them about the dead guy from the Netherlands who walked into the building at 7:30 this morning, and his veins ruptured. That was at 7:30 in the morning? Busy office! Walter theorizes vasculitis, or an arteriovenous fistula, which is an abnormal channel between the vessels resulting in swelling of the veins. "Until they rupture?" asks Astrid. No, not usually, admits Walter. "But then that's why we're here, I imagine," he adds, as they walk towards the doors of the building, just as a very sick-looking bike courier tries to get out. Walter instinctively holds the door shut upon seeing the man's face just as the veins start to rupture, and the courier spews blood all over the other side of the clear glass doors, which you'd think might be gross, but I did spend a year in residence at university.
Walter's excitement over the case has completely darkened. "This building must be quarantined immediately. No one goes in or out. I believe we have a contagion on our hands," he says. Just then, Olivia and Peter come down the stairs. For anyone who doesn't understand what quarantine or "no one goes in or out" means, Astrid says Olivia and Peter will be trapped inside. Walter looks like he'd like to change his mind, but repeats the instruction to quarantine.
After the commercial break, a frantic Walter is on the phone with Peter, trying to find out more information about the dead Dutchman: "If I can find out where he came from, where he was, then I could begin to ascertain what could have infected him." Peter says they don't know, and Walter says the guy must have been coming to see someone there. Then Walter notices the CDC arrive. This does not seem to be good news to him.
While Astrid tries to console Walter outside, Vincent Ames is starting to get a little irritated with the quarantine, and then some of the other office folks are asking about Mike. Olivia confirms that Mike is dead, and then a bunch of them start bickering over who got the dead guy's blood on them, and then they notice the office airflow has been shut down, which Olivia says is protocol in case the virus is airborne. Then she says she wants everyone to divide into two groups: one that was near VandenKemp, one that wasn't. Nobody moves particularly quickly, and then Peter grumpily snaps at them to get a move on.
Outside, an Arnold McFadden, field director at the CDC, introduces himself to Broyles, acknowledges Broyles has two people inside, and asks i