Jack takes drastic measures to ensure that the NSC never finds out the truth about Sydney's murder of a Russian diplomat. But his actions place a heavy strain on Vaughn's marriage, as Lauren gets closer and closer to the truth about Sydney. Meanwhile, Sydney agrees to go on a mission with Sloane in order to thwart plans to obtain the operating system to a deadly weapon -- and she discovers an unlikely ally in the hunt for her missing two years.

The episode was rated 7.73 from 185 votes.

Sydney's search for her past leads to a jailed Sark, but their Q&A is cut short when he becomes the ransom for a pair of abducted CIA scientists, whose kidnappers may be tied to the murder of his father. Jack contacts an old friend of sorts for info on Sloane's new world-peace project, and Vaughn makes a decision about his future as an operative.

The episode was rated 7.76 from 186 votes.

Sydney and Jack warn a disbelieving Vaughn about their suspicions of Lauren being the CIA mole. Meanwhile, Bomani and Sark take possession of the Rambaldi machine, Sydney and Vaughn must stop a Covenant virus that's crippling medical facilities around the world, Sloane's secret is revealed to Jack, and Bomani begins to lose faith in Lauren's ability to carry out her Covenant missions.

The episode was rated 7.77 from 175 votes.

Sydney attempts to rescue Dixon's kids after they are kidnapped by Sark, Lauren's status as a double agent is put to the test when she learns that she has to work with her father, and Sloane is framed as a CIA mole.

The episode was rated 7.77 from 182 votes.

After discovering the identity of the Rambaldi "Passenger," Sydney and Jack seek the aid of Sloane, to track the "Passenger" down. Meanwhile, after learning a secret about his father from Thomas Brill, Vaughn is kidnapped and tortured by Lauren and Sark, who are about to track "The Passenger" down themselves.

The episode was rated 7.78 from 178 votes.

With the aid of Katya Derevko and CIA imprisoned security systems designer Toni Cummings, Sydney and Vaughn attempt to track down Sloane and Nadia. But Lauren and Sark are also in hot pursuit of them in order to uncover the secrets of Rambaldi. Meanwhile, Vaughn's obsession with tracking down Lauren is beginning to consume him, Sydney and Vaughn turn the tables on an old foe, and Katya expresses her attraction to Jack.

The episode was rated 7.78 from 170 votes.

After finding out that Lauren is working for the Covenant, Vaughn is told to keep up the façade of a happy marriage in order to keep tabs on his wife's activities. But he's in for a shock when he uncovers the truth about Lauren's mother, Olivia. Meanwhile, Jack refuses to help exonerate Sloane of his crimes and put in motion a stay of execution, and a monk discloses the identity of the Rambaldi "Passenger" to Sydney.

The episode was rated 7.79 from 182 votes.

Sydney and Vaughn must convince bomb maker Daniel Ryan that they are part of The Covenant in order to find out where he has hidden one of his devices. But Sydney discovers that her ties to the bomber could lead him on a suicide mission.

The episode was rated 7.84 from 177 votes.

After making a shocking discovery in the desert, Sydney agrees to submit to an experimental procedure conducted by an eccentric doctor, designed to retrieve her lost memories. But while Jack and Vaughn look on, Sydney's mind proves surprisingly resistant to letting her remember her missing time -- and the process of recovering it could end up killing her. Meanwhile, Lauren makes a great sacrifice in order to make her alibi believable to Lindsey after breaking Sydney out of NSC custody, and Sloane finds himself boxed in by an unlikely enemy -- one who wants to see Sydney Bristow eliminated permanently

The episode was rated 7.86 from 202 votes.

When Sydney is taken into custody by the NSC, Jack and Vaughn have no choice but to ally themselves with Sloane to rescue her. But with only hours to spare before she is forced to undergo a radical surgery to recover her memories, they must put togther an extraction team, headed by freelance operative Brill (Richard Roundtree, "Shaft"). Meanwhile, Lauren faces an impossible choice -- side with the NSC, who she wants to believe is doing the right thing, or with her husband.

The episode was rated 7.88 from 193 votes.

Jack contacts a mysterious woman with ties to Irina to help him free Sydney and Vaughn, who have been captured and face a North Korean firing squad. But Jack is faced with a curious conundrum when the woman tells him that she will not put the rescue plan in motion until he fulfills a favor - assassinate Sloane.

The episode was rated 7.89 from 179 votes.

Sydney tries to piece together the last two years of her life and discovers the fates of her friends and family. She confronts Vaughn about his marriage and learns the shocking fates of Jack and Sloane. Meanwhile, she is granted temporary CIA clearance on a case that may help her regain her memory.

The episode was rated 7.91 from 204 votes.

Sydney finally learns the shocking truth about her missing two years from an unlikely source.

The episode was rated 7.92 from 190 votes.

The identity of the mysterious "St. Aidan" forces Sydney to pull a stunned Will out of witness protection. But the pursuit sends the two old friends on a collision course with Allison -- the woman who ruined both their lives. Meanwhile, a zealous Lindsey arrests Jack and Vaughn as conspirators in Sydney's escape from NSC custody, Sloane, still under pressure from Lindsey, puts a plan in motion to eliminate Sydney, and Dr. Brezzel has an unpleasant run-in with Sark.

The episode was rated 7.96 from 191 votes.

Lauren stages a stunning betrayal to steal classified materials from the CIA. Meanwhile, Vaughn comes face to face with his darkest demons in pursuit of his wife; Nadia must decide whether or not she can trust her father, Sloane, in the pursuit of Rambaldi's most priceless artifact; and Sydney receives a shattering revelation that will make her question everything - and everyone - she thought she could trust.

The episode was rated 7.99 from 175 votes.