Sydney and Jack must find a way to keep Sloane and Irina from putting their deadly plan into action.

Sloane takes Marshall and Rachel hostage in order to discover a crucial clue to Rambaldi's ultimate endgame, as Sydney, Vaughn and APO race to stop him.

Sydney must stay undercover and partner with Sark to track down Rambaldi's final clue before Prophet Five finds it. Meanwhile, Vaughn sees daughter Isabelle for the first time, and Rachel discovers Tom's secret.

Sydney must beat arch-nemesis Anna Espinosa to the punch when a mysterious chip found planted in Renee is tied to Vaughn. Meanwhile, Sloane struggles with ghostly visions while working for Prophet Five.

Sloane is distressed to learn that Prophet Five's cure for Nadia is just as likely to kill her. Meanwhile, the search for Anna Espinosa continues, Rambaldi's prophetic Page 47 resurfaces, and Sydney offers Renee a job at APO.

As part of a plan to bring Sydney back into the field for Prophet Five's own purposes, Peyton has Anna Espinova kidnap Will Tippin.

Irina returns and claiming to want to help, convinces Jack and Sydney to take her on a mission to retrieve The Horizon.

Marshall recovers an emergency transmission from Sydney but it's deleted by a Langley insider before he could listen to it - meaning Prophet Five has infiltrated the CIA.

Hoping to gain information from her, Prophet Five capture Sydney and makes her relive moments of her past with Vaughn.

Unaware of who the other really is, Rachel and Sark fall for each other while both undercover.

Sloane confesses to Jack and Sydney that he had been working with Dean, as they come up with a plan to trap him.

Sydney must guide a nervous and pensive Rachel on her first solo mission. Sloane must decide whether or not to betray the trust he's recently earned with APO.

Sloane asks to be reinstated in APO so he can find a cure for Nadia. Syd and Tom meet Renee in Marseilles and return to her loft, where the now revived but disoriented man from the box suprises them.

A shipping crane lifts Sydney's car hundreds of feet off the ground. Sydney answers her phone - it's Gordon Dean saying he wants Mockingbird.

The team interrogates Rachel, a hacker working for Dean, as Sydney realizes they have a lot of similarities.

Sydney visits Sloane in his jail cell. Jack meets with Thomas Grace, a new agent he is recruiting into APO.

After learning that the man she has known as Michael Vaughn is under investigation and suspected of being a double agent, Sydney begins to question whether their business and personal relationship over the years had all been a lie.