A routine flight takeoff is interrupted by an anxious passenger, a woman who knows more than she’s saying, and a distant scream on the other end of the phone.

As the plane takes off, Jake tries desperately to text his mother, while Marcus vomits into a bag as his wife tries to comfort him.

The flight attendants begin to serve drinks throughout the cabin, and Jake has a short discussion with Connie about how he ended up on the plane without his mother.

Marcus starts to feel sick and urgently has to use the lavatory. His wife claims, he suffers from reflux.

The passengers are asked to prepare for the descent to Phoenix. As Marcus is still in the bathroom, the flight attendants urge him to come out.

As a blackout continues to roll across Phoenix, Alex urges Deirdre not to open the door. Suddenly, the bathroom door opens and Marcus falls out, unconscious.

The passengers learn what they're up against as the plane re-routes from Phoenix to Los Angeles.

Anthony, an U.S. Air Marshal demands that all the passengers return to their seats, despite Alex's warning that Marcus is now dangerous.

Marcus has turned into a walker and after a struggle the group shoves him back into the bathroom. Once he is secured they notice blood on themselves and determine that Deirdre was scratched on the arm.

Alex tells Anthony to secure Deirdre since she has been bit and will turn like Marcus. Alex tries to convince the Captain to land the plane, but all the cities are experiencing power loss.

Suzanne mourns the loss of her husband from outside the compartment door where he is held while he continues to bang on the door from the other side. Anthony tends to Deirdre's bite wound.

When Suzanne's husband stops banging on the door, she fears that it is a sign he is dying. She then unlocks the cabin bathroom door releasing him into the isle where all chaos breaks loose.

With Marcus on the loose, Jake finds a knitting needle and hands it to Alex who takes care of the situation. Once it's done, the group notices a crack has formed in one of the plane's windows and it's starting to spread.

Suzanne who has been bitten is comforted by Deirdre while Alex takes matters into her own hands concerning how to deal with the bite wound. The window which has been slowly cracking finally completely shatters.

As the airplane cabin depressurized, the passengers struggle to find available seats and strap on oxygen masks. Alex and Jake buckle in next to each other and she makes a startling revelation to him.