Some say 24 peaked during its Emmy-winning fifth season, while others claim it irreversibly lost its mojo after the wildly misguided sixth season. Others still insist the series finale lacked teeth, setting up a film rather than bringing Jack Bauer's journey to a close.

As of tonight's 24: Live Another Day premiere, those notions will be put to the test — and for many fans, put to rest.

With Live Another Day, Fox and the creative team behind 24 offer up one more round of action, albeit in a new format. Rather than sticking with the drama's standard 24-episode order, Live Another Day is just 12 hours long, unfolding over the course of one very bad day.

It's an unexpected shift for a show called 24, which takes its name from its very specific premise of chronicling a 24-hour period over the course of a season. But it's a necessary shift: From as far back as Season 1, 24 suffered from overstuffed stories, a response to the mandate to fill out every minute of Bauer's day. The result: inexplicable amnesia subplots, mountain lions, and basically everything having to do with Kim Bauer.

Immediately, Live Another Day cuts out all of that fat. The two-hour premiere is a lean, mean return to the world of 24, without a second wasted. Even the most superfluous-seeming storyline has a purpose; for instance, future Star Wars actor John Boyega plays an Air Force pilot who appears to be on the fringe of the main story, but quickly gets sucked into the central action by the end of the first hour. Another thread, involving a shady computer hacker, follows that same path. Unlike seasons past, the B and C plots of Live Another Day matter, at least as far as the first two episodes are concerned.

And that's because there's no time to waste. The tightened episode order still keeps the real-time element intact; Live Another Day will skip hours here and there, allowing Bauer to ride a train from one location to another without having to come up with some contrived train-ride action scene. But otherwise, it's the same 24 as it ever was: a story that moves at a breakneck pace, charting minute after minute of Bauer's brutal day.

Right away, Live Another Day answers the all-important question: Where is Jack Bauer? Four years have passed since the end of Season 8, and that time is reflected in the world of the series. Bauer has been on the run all that time, hiding in Eastern Europe, a fugitive from justice after his Day Eight killing spree that claimed the life of a Russian diplomat. At 11 a.m., Bauer resurfaces in London, and immediately falls into the CIA's hands. It's almost as if he wanted to be caught.

It turns out that Bauer isn't the only familiar face in London at the start of Live Another Day. The city also plays host to U.S. President James Heller (William Devane), former Secretary of Defense and the father of Bauer's old flame Audrey (Kim Raver). Heller, harboring a tragic secret known only to Audrey and her new husband (and Heller's chief of staff) Mark Boudreau (Tate Donovan), is in London to work with British Prime Minister Davies (Stephen Fry) on innovative drone technology that could revolutionize modern warfare. But a horrific act committed in Afghanistan, purportedly by American forces, threatens to end Heller and Davies' truce before it even begins.

With Heller in London at the same time as Jack, the CIA believes Bauer's reemergence could have something to do with a plot against the President's life. And while they have the wrong man in custody, their theory isn't off the mark. Bauer feels he owes it to Heller to stop the plot against his life; but beyond that, the assassination of a U.S. President on foreign soil could spark an international incident on the scale of a new World War.

The stakes are high right away when Live Another Day begins, but at the same time, the show feels more personal than it's felt since Season 5, which began with President David Palmer's assassination. Like that season, Live Another Day centers on a threat against a familiar character's life. It has further-reaching implications, thanks to ideas of drone warfare and the international setting. But immediately, Live Another Day carries more weight because of its focus on the endangered Heller, someone that 24 viewers have come to know and love over the years.

The event series also feels more personal because of Bauer himself. It's an entirely new spin on Kiefer Sutherland's iconic character. Viewers are used to seeing Jack on the rocks and at the bottom of a pit of despair. But here, Jack isn't grieving his wife's death, and he isn't at peace with his self-imposed exile. He's angry; he's a shell of his former self. He's four years removed from the hero who stopped nuclear threats and high-level assassinations like clockwork. Now, Jack's a man who feels left behind and disenfranchised by the people he sacrificed everything to protect. As a result, he's darker and deadlier — and above all, more unpredictable than ever.

It's unclear what Bauer did to survive during his time away from America, but the premiere implies that whatever he's been up to hasn't been pretty. Can Jack come back from the brink of violent rage and disillusionment? That question is very much at the heart of the premiere and, presumably, Live Another Day at large.

Even if he feels abandoned, Jack isn't entirely alone, thanks to the return of Chloe O'Brian, the fan-favorite computer hacker played by Mary Lynn Rajskub. Like Jack, Chloe isn't the picture of patriotism she used to be. She's undergone her own trauma and transformation, although the details are a bit murkier. In fact, saying too much about Chloe ruins one of the great surprises of the Live Another Day premiere. But like Jack, Chloe is a changed character with mysteries of her own.

Jack has always been the face of 24, and Chloe has been right by his side since Season 3. However, 24 doesn't work without strong supporting characters working that ticking clock. Live Another Day boasts 10 series regulars, with at least four other notable guest stars. It's a massive cast, and just four of them are familiar quantities from the 24 days of yore. The revival deserves credit for letting the viewer learn and care about each of the brand new characters in just two hours, with only one or two getting the short end of the stick.

Of the newcomers, Yvonne Strahovski is the standout. She plays Kate Morgan, a CIA agent scheduled to transfer out of the London office by the end of the week. She's nursing wounds of her own from a personal and professional betrayal that's rattled her ability to do her job. The emergence of Bauer jolts Morgan back to life, giving her an unexpected shot at redemption.

The rest of the CIA office is filled with character types that are all too familiar to 24 fans. Benjamin Bratt plays Steve Navarro, the buttoned-up station director with the dry personality of Bill Buchanan and the bullheadedness of Ryan Chappelle. Gbenga Akinnagbe plays Erik Ritter, Morgan's eager replacement, a hotheaded agent who brings Chase Edmunds to mind. Finally, there's Giles Matthey as Jordan Reed, a computer tech with extreme loyalty to Morgan, and shades of Milo Pressman. Even if these are familiar types, the characters stand out thanks to fine performances, from Strahovski, Bratt and Akinnagbe in particular; the jury's still out on Matthey, as the premiere doesn't give him too much to do.

Beyond the CIA, Tate Donovan fuels the fires of the political storyline, as a man with deep personal and professional ties to President Heller. He's connected to Bauer, too. As Boudreau, Donovan's character isn't only afraid of what Bauer might do to Heller, but what Bauer might do to Audrey's psyche, considering the role he played in Audrey's catatonic state in season six. Donovan shoulders the stress of the day with a burning, teeth-gnashing energy that fits right at home on 24. It's almost a wonder that the actor hasn't appeared on the show already.

In short, Live Another Day works. It boasts a strong cast, a compelling plot, an even more compelling new twist on Bauer, and a storytelling format that somehow moves faster than ever before. Like Bauer, it took four years for 24 to reemerge from hiding — and like Bauer, it's returned with the same ferocity and danger that made 24 a can't-miss series in its glory days.

24: Live Another Day premieres tonight at 8 ET/PT on Fox.