Suddenly, TV screens in the APO office display news reports about Sovogda, a Russian city in chaos. Marshall then receives a video feed from a hacker in Moscow, showing raw footage of anarchy. The footage reveals a giant red ball hovering in the sky - Rambaldi's Mueller Device.

The team believes that Sloane and Elena have activated the Rambaldi device in Sovogda, which resulted in unbridled aggression in its citizens. They conclude that the city's contaminated water supply combined with the chemical properties of the orchid made the residents susceptible to the Mueller device. The only solution is to disarm the device properly -- and Irina Derevko, who is being held prisoner by her sister, is the only one who can do it. They need to force Lucien Nisard to reveal her location.

Vaughn comforts Sydney and tells her that they're going to get through this. As he was about to bring out the ring and propose, Marshall arrives and says that it's time to leave.

They arrive at a dance club in Ibiza, where Sydney goes in with Vaughn and spots Nisard. Syd and Vaughn make out -- and as Syd makes eye contact with Nisard, she invites him to join them. They go to the bathroom where Sydney and Vaughn transmit his PDA contents to Marshall. When they find that the Helix Protocol is mentioned, Syd dunks his head in the toilet and asks about Irina. Nisard confesses that Elena doubled Irina and confirms that the real Irina Derevko is in Guatemala.

When Syd and Nadia arrive in Tikal, Guatemala, Jack guides them via a satellite layout of the camp until they locate an underground cell. They open the hatch, finding Irina.

"I knew you'd come," Irina tells Sydney, and they escape. As guards chase them, Sydney walks into a trap and is strung upside-down. Irina rescues Sydney while Nadia holds the guards off. They run to escape as more guards arrive. Syd throws a grenade at them and, along with Irina and Nadia, escapes on a raft.

On the plane, they tell Irina that Elena and Sloane have enacted their plan. Irina shares that she found a Rambaldi manuscript - Il Diluvio - which revealed Rambaldi's desire for a complete cleansing through apocalypse. Though Irina destroyed the manuscript, Elena tortured her to get the info, forcing her into dozens of cardiac arrests. Irina admits that she finally broke and told Elena everything. Now, they must go to Sovogda and stop them before they move to another city.

Irina breaks down when she realizes whom Nadia is. Later, as they look over a map, they agree that Sloane and Elena must be somewhere in Sovogda but safe from the Mueller device. Suddenly, Jack gets a call from the pilot, and their plane is diverted by official orders from Langley.

As they land, police cars arrive and arrest Irina, who is still a fugitive. Syd goes to Director Chase and argues that Irina is the only one who can help them. Chase says the matter will be resolved in a few hours by a Russian air strike. Syd points out that this will release toxins in the atmosphere and results will be catastrophic. She begs Chase to trust her.

As the team prepares to parachute into Sovogda, Vaughn pulls Sydney aside and says that he wants to spend the rest of his life with her. He gives her the ring and asks her to marry him. Overwhelmed and delighted, Sydney kisses him and tells him to ask her again on the beach.

The plane's rear door opens and Irina, Jack, Vaughn, Nadia and Sydney jump out.