CTU-- the government agency with the hippest clothes and technology, the messiest private lives and the highest mortality rate in America. 24-- the TV show that you can't stop watching even when you don't believe a moment of it. And Jack Bauer-- the Id of post-9/11 America. Here's a rundown on five years of bad days for Jack Bauer:

SEASON 1-- Investigating an assassination plot against a black presidential candidate, Jack Bauer is forced to become the assassin himself by baddies holding his daughter Kim. This is really the only season to live up to the premise of realistic real time-- in later seasons CTU operatives can drive halfway across Los Angeles in a commercial break-- and that realism pays terrific dividends in certain scenes, as when Jack's wife spends time in the company of a guy who may be another concerned parent or not... and it takes a good two or three episodes to find out for sure. Casting is excellent-- why hasn't bad guy Michael Massie gotten more work?-- and the soap operatic aspects (Jack had an affair with one of his coworkers, which is going to blow up in a big way in both his personal and professional lives) enhance rather than detract from the suspense, all the way to a gut-punch ending which is one of the most shocking in TV history. A terrific season which earned the show a lot of viewer loyalty.

SEASON 2-- The black candidate in Season 1 is now President Palmer, middle easterners want to explode a nuke in LA, and President Palmer's weak handling of the crisis leads to an attempt by members of his cabinet to remove him from office. There are good villains in the terrorists, Xander Berkeley's bureaucratic boss, and especially Penny Johnson Jerald's scheming First Lady, but the CTU office romance of Tony and Michelle is tedious, and the efforts to find a way to put Kim in peril get steadily more ridiculous (two words-- mountain lion! Six more words-- Kevin Dillon as a survivalist kook!) The biggest problem is that the character of President Palmer is so poorly conceived; we're supposed to see him as noble and Lincolnesque compared to the schemers around him, but in fact he always makes the worst choices for the most pompous reasons, making it hard for others to support him, for CTU to do its job-- and for viewers to sympathize with him in the internecine struggle.

SEASON 3-- A couple of drug cartel-running brothers (who Jack has been undercover with) plot to release a biological weapon in LA. This season starts disastrously, with far too much soap-operatic attention paid to younger characters presumably shoved into the cast at the network's insistence. (Call it Dawson's 24.) Having written themselves into a hole, the writers throw a Hail Mary pass at the 8 hour mark which changes everything for the better (despite the fact that it contradicts much of what we've seen). The rest of the season continues reasonably suspensefully, though there are still absurdities (this season's mountain lion is a baby hidden under a desk at CTU!), and the amount of screen time devoted to slow death from infection and/or the threatened torture of captives makes this a deeply unpleasant season to watch. On the plus side, it does bring back both of the show's great villainesses to date, and both actresses take full advantage of the opportunity to show off their highly hissable characters in an encore. And it introduces the best supporting character at CTU ever-- Mary Lynn Rajskub's computer whiz Chloe, who's brilliant, but full of bad attitude.

SEASON 4-- Middle eastern terrorists get hold of a device which allows them to cause nuclear plant meltdowns. The best season since the first, this one does a terrific job of exploring all the fears, issues and character types which had been in the public consciousness since 9/11. Arnold Vosloo is the main villain, a kind of clean-shaven Bin Laden, but much of the plot revolves around a seemingly Americanized Arab-American family who are in fact moles preparing for a suicide attack; the dramatization of jihadist attitudes through the fanatical father, conflicted mother and thoroughly westernized son is quite powerful. Likewise, Jack's frequent resort to torture is explored as a moral issue with no easy answers.

The season isn't perfect-- THIS season's mountain lion is the schizophrenic daughter of the new CTU director who's being treated at CTU (!!!), a subplot that removes the fine actress Alberta Watson from CTU far too early in the season; and Jack's romance with the daughter of a Rumsfeld-like Secretary of Defense is drippy-- but all in all it's a powerful and thought- provoking season, and serves to introduce the third, and by far the most interesting, presidential character in the series, Gregory Itzin's weaselly President Logan.

SEASON 5-- Jack, living under an assumed name, gets pulled back in when Chechen terrorists try to disrupt the signing of a treaty with the Russian president by threatening a nerve gas attack. The real stars of this season are Gregory Itzin as the sleazy President Logan and Jean Smart as his mentally disturbed, but no dummy, First Lady, and the game that's played out between them as the conspiracy twists like a pretzel is great fun. At the same time we get Peter Weller as Jack's ex-boss, now possibly a conspirator, which is as close as we're likely to get to a Star Trek-like Good Jack Bauer fighting Bad Jack Bauer. Not as convincing as Season 4, and the writers prove far too willing to kill off promising characters for the (diminishing) shock value rather than develop them to their fullest, but the performances of Itzin and Smart make this deliciously watchable TV up to the very last twist.