Artie patrols the empty hallways of the high school. He hears a noise and turns.
Alicia looks for Matt at his house and finds the place in disarray. She gasps when she enters the living room.
Fleeing the site of their run-in with Calvin, Travis, Madison and Nick speed home in the truck. They decide they should evacuate to the desert. Travis leaves a voicemail for Chris, telling him it’s an emergency. Madison calls Alicia and learns that she’s with Matt, who is home alone with a fever. Madison urges Alicia to stay away from Matt until they arrive.
At Matt’s house, Madison and Travis find Alicia wiping Matt’s brow, refusing to leave his side despite the possibility of infection. Travis finds a large bite on Matt’s neck. Realizing the gravity of the situation, Matt urges Alicia to leave with her parents.
Nick meanwhile rifles through Matt’s bathroom drawers, desperately looking for drugs.
Chris boards a city bus, ignoring the phone call from Travis. The bus hits a traffic jam. A man runs onto the bus and announces that police shot a homeless man up ahead.
Travis, Madison, Nick and Alicia arrive home. Mrs. Cruz, a neighbor, invites them to her daughter’s birthday party. Travis sees another neighbor urgently packing his car.
Inside, Nick insists Madison tell Mrs. Cruz about the virus. “I’m about to step into a world of shit,” Nick tells Madison, warning her about his upcoming withdrawal symptoms.
Unable to reach Liza or Chris by phone, Travis leaves for Liza’s house to pick them up. He urges Madison to go to the desert without him if necessary, promising to catch up later. Madison refuses.
Travis gets through to Liza and says that he’s coming over. Liza hangs up on him, angry that he’s reneging on their custody settlement and trying to take Chris on a non-designated weekend. Stuck in traffic, Travis notices a cop loading his trunk with bottled water.
Chris joins a mob that’s gathered around the homeless man’s body. He sees an EMT worker treat a cop with a bite wound. Chris whips out his video camera and begins filming as the mob yells at the cops for shooting an unarmed man.
Nick writhes on the couch in the throes of withdrawal while Madison unsuccessfully tries to reach his doctor for a methadone prescription. Desperate, she leaves the house and orders Alicia to stay put.
Madison drives to the high school and grabs a bag of OxyContin from a supply closet filled with items confiscated from students. Tobias appears, catching her by surprise, and asks for his knife back.
Alicia leaves the house to check on Matt but Nick pleads with her to stay, saying Matt will kill her. "You don't know what it makes people do," Nick pleads. She runs back inside when Nick has a grand mal seizure and starts to choke on his own vomit.
Travis arrives at Liza’s house and tells her about the virus, saying it makes people violent. He calls Chris from Liza’s phone. Chris answers but quickly hangs up, telling Travis that he’s part of a protest. Travis and Liza figure out Chris’ location after seeing news coverage of the shooting on TV.
Nick thanks Alicia as she scrubs vomit from the floor. “I hate you,” she says.
In the school cafeteria, Madison helps Tobias stock up on canned food. They’re wheeling a cart of food through the school when they hear a growl on the audio switchboard, followed by the blaring of the school’s metal detector. They run into Artie, who has turned. Not believing what she's seeing, Madison approaches her boss, who lunges at her.
Tobias jumps in the middle and stabs Artie, but they're thrown down the stairs and Artie lands on top of Tobias. Madison rescues Tobias by bashing Artie in the head with a fire extinguisher and she and Tobias flee together.
Travis and Liza find Chris at the protest as workers in hazmat suits and riot police show up. An Infected woman wanders onto the scene and the police open fire, sending the mob into chaos.
Travis, Liza and Chris flee onto a street in the midst of a full-blown riot. A barber, Daniel Salazar, is shooing his last customer out when Travis begs him for shelter. Daniel is reluctant, but his wife Griselda motions to allow them inside. As mayhem descends on the street, Daniel lowers the shop’s metal shutters. Travis thanks him, meets his daughter Ofelia and explains that victims of the virus don’t die. “They come back,” he says.
Madison drops Tobias off at his house. She offers to let him stay with her until the crisis ends. Tobias declines. "This doesn't end," he says.
Madison goes home and gives Nick two pills. While washing her blood-soaked jacket in the bathroom, she breaks down in tears. Travis calls to tell her he’s marooned and again urges her to go to the desert without him. The phone connection fails.
Madison and Alicia hear a scream outside. They watch Mrs. Cruz’s husband attack her in her front yard. “Don’t look,” Madison says, drawing the shades. Alicia starts to run outside to help, but Madison blocks the door.
At Salazar's, Griselda lights prayer candles while her family and Travis’s gather together.