MY wife and I were late converts to "24," becoming hooked only a year ago, after our son gave us a boxed set of the first season on DVD. Innocently, we slipped in the first disc, listened to Kiefer Sutherland announce, "I'm federal agent Jack Bauer, and today is the longest day of my life," and then for a week we seldom left the couch, bingeing sometimes on five or six episodes at a time." "Another one?" we'd say. "Well, maybe just one."

DVD still seems the best way to watch any of the new, extended-plotline series: not just "24," but also "Lost," "Alias" and "The Wire." You don't have to wait a fretful week to find out what happens next. You can watch (and pause to bathe occasionally and take nourishment) whenever you want, and by skipping the commercials you save about 15 minutes of every hour, which makes this sort of watching seem more virtuous than the other, network-controlled kind.

At the moment we're watching Season 2 of "24" on DVD, in carefully measured doses, while also trying to follow Season 5 in once-a-week real time. Keeping the two story lines straight is harder than you might think and has resulted in frequent episodes of conjugal head shaking. What are we dealing with here? my wife and I have to remind ourselves periodically. Nuclear, biological or chemical? Bombs or nerve gas? Who are the terrorists, Central Asians or Middle Easterners? Is Jack Bauer in the bunker or in the cargo hold of an airliner? And where is Jack's annoying daughter, Kim? Is she still an au pair for the guy who beats his child, or is she with that creepy older fellow, the psychologist? And what happened to that child, anyway? She can't still be cowering in the cardboard box?

Sorting all this out ought to be easier, considering that the administrations depicted in these two seasons couldn't be more different. In Season 2 the calm and judicious David Palmer is still president � by far the best imaginary chief executive this country has ever had � while in Season 5 he's been replaced by the loathsome Charles Logan, who slinks every week to new levels of sweaty Nixonian duplicity. Just recently we learned that he actually engineered Palmer's assassination.

On the other hand there's a lot of overlap between the two administrations. The bullet-headed Mike Novick, who used to be Palmer's chief of staff, now works for Logan, and to make matters more confusing he's so much a Dick Cheney lookalike that you keep expecting him to want to call in the military when in fact he's one of the few decent people in that entire administration. The same is true of Logan's flaky, pill-popping wife, Martha, who is clearly meant to remind us of another Nixonian figure, Martha Mitchell, but is a far steadier influence than Palmer's grasping and ambitious wife, Sherry.

You can't pick up any useful clues as to where you are in the series by merely taking note of who is in charge over at C.T.U., the counter-terrorist unit to which Jack is attached, because the place is always in upheaval, with one new government flunky after another coming in and locking the unit down so the "protocols" can be changed, whatever they are. Chloe, her face scrunched up, punching codes into her laptop, is the one constant.

Meanwhile the same kinds of things keep happening from season to season. Canisters with ticking digital clocks; Jack going solo, racing around in an SUV and yelling on his cellphone; C.T.U. itself under attack. There is treachery in the White House, and sooner or later a suspect turns up who won't talk and, since the fate of the country is at stake, needs a little chemical encouragement. (With Christopher Henderson, though, the hard case in Season 5, it's odd that no one has noticed he's played by Peter Weller, formerly the Robocop; he's half machine, that is, and instead of drugs, the interrogators should be using a welding torch.)

From season to season, the shows also look and feel much alike: the same dark lighting and lingering close-ups; the same slow buildup to the cliff-hanging scene breaks, punctuated by that ominous da-dum, da-dum, da-dum. This is merely to say that, like so many TV series, even very good TV series, "24" is formulaic. There are only so many variations that the creators, Robert Cochran and Joel Surnow, can elaborate on the theme of the renegade agent who in just 24 hours � or 24 less-than-hourlong episodes � rescues his country from an overwhelming threat, and when they hit upon something that works they tend to go back to it.