The threat to the United States in Season 5's white-knuckle day is Russian separatists armed with weaponized nerve gas and led by Vladimir Bierko (Julian Sands). Inciting their ire is an arms and mutual defense treaty that Russian president Yuri Suvarov (Nick Jameson) plans on signing with the U.S. and duplicitous president Charles Logan (Gregory Itzin). As Day 5 begins, Jack Bauer (Kiefer Sutherland), who faked his own demise at the close of last season, is working at an oil refinery in California under the name Frank Flynn. He returns from his self-imposed exile to fight the good fight after an assassination rocks the nation and he finds himself framed for it and several other crimes. Jack is also reunited with former love interest Audrey Raines (Kim Raver), but tumult continues to follow them. Meanwhile at CTU, there's a new man brought in to oversee operations, Lynn McGill (Sean Astin), and once again, there's a mole in the ranks. A significant subplot centers on Christopher Henderson (Peter Weller), Jack's mentor-turned-nemesis who has information that can help Jack thwart the Russians. Another thread follows First Lady Martha Logan (Jean Smart), who grows increasingly disdainful of her husband's actions in office.

With a new day comes a new leader for the sixth season, as Wayne Palmer (DB Woodside), brother of former president David Palmer, has taken the reins from the corrupt Charles Logan (Gregory Itzin). But President Palmer has little time to celebrate his election, as America faces yet another grave threat, this one from Islamic terrorist Abu Fayed (Adoni Maropis). By way of introduction, Fayed orders suicide bombings of 10 U.S. cities over a period of 11 weeks. But he's just getting warmed up-before Day 6 comes to a close, the threat goes nuclear. Trying to prevent further bloodshed, as always, is Jack Bauer (Kiefer Sutherland). Out of the frying pan and into the fire, Jack is freed after months of torture in a Chinese prison, only to be handed over to Fayed in exchange for seemingly valuable intel. Tackling the day's dangers on the CTU front are new personnel additions Mike Doyle (Rick Schroder), who replaces the fallen Curtis Manning as director of field operations, and Agent Milo Pressman (Eric Balfour), who has a history of butting heads with his new boss. Day 6 also provides the first glimpse of Jack's blood relatives, his father Phillip (James Cromwell) and brother Graem (Paul McCrane). But it's far from a touching family reunion, as one of Jack's toughest challenges is determining where the other Bauers' loyalties lie. Several new faces make their way to 1600 Pennsylvania Ave., including steely vice president Noah Daniels (Powers Boothe) and presidential advisers Reed Pollock (Chad Lowe) and Thomas Lennox (Peter MacNicol), each of whom has his own agenda. Making a surprise return later in the day are former president Logan, his ex-wife Martha (Jean Smart), and former Secret Service agent Aaron Pierce (Glenn Morshower), all of whom play brief but pivotal roles in the season's developments.