CTU deal with a deadly virus threat that would be released in Los Angeles. Jack's nemesis Nina Myers is also seen, while he is trying to break his heroin addiction after his undercover operation with Ramon and Hector Salazar. Jack's colleagues suspect that his difficulty quitting is related to the death of his wife Teri at the end of the first season. Jack has a new protege in tow, Chase Edmunds, but things take a turn for the worse when it is revealed Chase is seeing his daughter Kim, and it causes tension among the three of them. President Palmer is seeking re-election against Senator John Keeler, but his campaign turns sour after one of his major backers, Alan Milliken, discovers that Palmer's brother, Wayne, has been sleeping with Julia Milliken, Alan's wife. Palmer's campaign suffers a major blow when revelations come out about his girlfriend and personal physician Anne Packard. The president turns to his ex-wife Sherry to deal with Milliken. Sherry takes it all a step too far when she kills Milliken by not allowing him his medication, which he needs to stay alive. Despite David Palmer's best cover-up efforts, Keeler uses it as leverage in the campaign. Toward the end of the day, Julia kills Sherry before taking her own life, and Palmer decides not to seek re-election. Back at CTU, it turns out that Tony Almeida, Gael Ortega and Jack have been working undercover on a sting operation. Chase is initially unaware of the situation and attempts to "rescue" Jack, who is being held captive by the Salazars. Tony recovers from a gunshot wound to the neck, to return as head of CTU, with many doubting his abilities. Nina comes in just as Jack and the Salazars are trying to get hold of the virus from Michael Amador, but he plays them all for fools. After Nina is captured by CTU and interrogated, she makes a daring escape attempt only to be found by Kim. Jack comes in and finally gets revenge for the death of his wife Teri. Amador meets with his accomplice Marcus Alvers, who later plants some of the virus in a hotel ventilation system. When Michelle Dessler captures Alvers, he reveals that the mastermind of the day's events is a man from Jack's past named Stephen Saunders. Gael is killed soon after being exposed to the virus and Michelle has to deal