The story of this season takes place three years after the last season. In this season, Tony (Carlos Bernard) and Michelle (Reiko Aylesworth) got married and became the director of CTU, and Jack's (Kiefer Sutherland) daughter Kim also joined CTU as an intelligence analyst. The plot begins with a body thrown outside the Los Angeles Health Center and infected with a deadly virus. In order to get the US government to release his brother, a Mexican drug lord threatened to use a deadly virus. Jack also embarked on the road of anti-terrorism investigation. In this season, Jack's investigation was not smooth. In order to get into the drug dealers, Jack did not hesitate to get addicted to drugs, which led to many difficulties in his investigation. In the White House, President Ballmer (Dennis Haysbert), who was re-elected, had a private doctor girlfriend around him after recovery, and the president's brother Wayne became his right-hand man. In the face of the pressure of re-election, he had to resolve this biochemical crisis. Can the president give Jack the same strong support he did in previous times?