Note that this summary (originally written by me for the Jack Bristow fanlisting) may contain spoilers.

Season 1

Sydney always thought her father sold airplane parts, but that was just a cover. He never sold airplane parts.

Sydney learned the truth when Jack helped her escape from SD-6 agents who were trying to kill her.

Sydney later found out that Jack is also a double agent, working with both SD-6 and the CIA.

When Jack learned that Sydney's fiance Danny was going to be killed by SD-6, Jack arranged for both Sydney and Danny to flee the country; unfortunately, Danny was killed before Jack could follow through on his plan.

However, Sydney's reporter friend Will Tippin discovered plane tickets for Danny and "Kate Jones" to leave the country; despite Sydney's pleas for him to leave that mystery alone, Will continued to investigate. Sloane, the SD-6 director, wanted to have Will killed, but Jack wanted to spare Sydney the loss of another friend. In disguise, Jack kidnapped Will and threatened his family. Convinced, Will decided to drop the story.

When a search for the information leak at SD-6 pointed to Sydney, Jack framed Russek, another SD-6 agent, as the "mole" to protect her. The frame worked to free Sydney but resulted in a torturous death for Russek

Sydney was stunned when Jack revealed that her mother, whom she knew as Laura Bristow, was actually KGB agent Irina Derevko, who was sent to the US to marry a CIA agent and steal information from him.

Sydney was in college to become a teacher, because she thought her mother was a teacher. After learning the truth, Sydney considered abandoning her studies, but Jack said that Sydney "could become the kind of teacher your students will always remember."

Later, Sydney discovered that her mother faked her death to escape capture, and Jack was shocked, to say the least. Sydney became obsessed with finding out what happened with her mother, which caused Jack to become angry/worried.

In an old video tape, Irina Derevko told her KGB superiors: "Every night for ten years I went through his briefcase. I eavesdropped on all of his private conversations. I planted listening devices on his clothing. He was blinded by his emotions. He knew nothing. I can tell you one thing: Jack Bristow was a fool."

A dangerous mission resulted in Sydney being captured. Handcuffed to a chair, she finds herself face-to-face with the criminal mastermind known as The Man: Irina Derevko!

Season 2

Irina demanded to know the name of Sydney's employer. When Sydney refused to tell her, Irina shot her in the shoulder. She then left, conveniently giving Sydney time to escape.

Not much later, all of the CIA was stunned when Irina turned herself in. Jack suspected her of having an ulterior motive, and he was repeatedly frustrated when the others were only too willing to believe her.

During her incarceration Irina assisted the CIA several times by providing information critical to their missions. She earned their trust enough to be allowed to go on a mission, but she took advantage of the opportunity and escaped.

Investigating Project Christmas, a program in which exceptional children are programmed to be spies, Sydney was devastated to learn that her father subjected her to the training. She was furious with him, but he later says that he only did it to make her strong. He never intended for her to lead a double life.

Mid-way through season two, Jack, Sydney and the CIA succeeded in bringing down SD-6. However, Sloane escaped, and it became clear that he still posed a threat.

At the end of season two, Sydney awoke in an alley in Hong Kong. Unaware of how she got there, she contacted the CIA who informed her that they had thought she was dead: she'd been missing for two years.

Season 3

While investigating Sydney's apparent death, Jack found proof that she was still alive. However, he was arrested by the National Security Council and put into solitary confinement for working with Irina. Jack later told Sydney that Irina was the only one he could trust.

After Sydney's return, she blackmailed the NSC director to obtain Jack's release from prison, and he returned to work at the CIA.

In Wittenburg, following a lead given to her by a villain, Sydney locates a certain bank box. In it, she finds top secret papers that tell of an "active project" that started on her birth date - with project manager Jack Bristow. Syd cries as she reads the documents. Jack suddenly appears, telling her that she was never supposed to have found them.

Season 4

Sydney revealed to Vaughn that the papers she found in Wittenburg were an official request from her father to assassinate Irina Derevko. The request was approved, and Irina is dead.

Again, the relationship between Sydney and Jack became strained, as she was furious with him for murdering her mother.

However, an oddly coincidental mission revealed another disturbing truth: Irina had hired a contract killer to murder Sydney! With Irina dead, the hit on Sydney had been cancelled. Jack had killed Irina to save Sydney.

Following a lead from Katya Derevko, Sydney learns that Irina was framed.

Jack and Sloane revealed that Elena Derevko, Irina's long-missing sister, has been tracking Sydney and Nadia. APO soon learns that Elena is working on something related to Rambaldi.

Apparently falling back into his Rambaldi obsession, Sloane finds Elena and offers to join her. While hunting for Sloane and Elena, Dixon finds someone else: Irina Derevko. He is proven correct when the team discovers that the woman Jack shot was a genetic double of Irina. Elena wanted everyone to believe her sister was dead. Jack, Sydney and Nadia find and free Irina. Irina explains that she had found the manuscript with instructions for assembling Rambaldi's final plan. She destroyed the manuscript but Elena tortured her until she revealed what she had read.

Soon, Elena puts her plan into action and she activates a large version of the Mueller Device over a Russian city. The city's residents, who drank water that was prepared with a chemical by Sloane during his previous Rambaldi quest, become extremely violent and the city is torn apart by the crazed mob. Irina, Jack, Vaughn, Nadia, and Sydney arrive to stop them.

On the ground, en route to the device, Nadia is separated from the others by a mob of crazed residents. She escapes from them only to be captured by one of Elena's men. When Nadia refuses to join her side, Elena injects her with the contaminated water.

Sloane shoots Elena's guards and joins the others with orders on how to stop her, but they don't trust him. They continue with their own plan, but Sloane assists them in gaining access to Elena. Sydney goes to the roof to disarm the device, but Nadia, in a trancelike state under the effects of the device, is guarding it. They fight. Ultimately Sloane saves Sydney by shooting Nadia. Irina talks Sydney through shutting down the device. The team makes it to Elena's secure chamber seconds before the water from the device destroys the building.

Waiting for pickup, Jack lets Irina go, despite her previous agreement to return to CIA custody after the mission.