There have been several obvious factors in the series success; the main one being the skill, which the creators have finely honed over the years, of keeping a constant-edge-of-your-seat tension running from episode to episode — constantly coming up with a stream of threats to rugged super-agent, Jack Bauer as he struggles to save the world over-and-over-again like some modern-day Sisyphus, forever doomed to push the same rock up the same mountain for eternity! When one looks again at Season One, it seems relatively slow-paced in comparison to later series (although it seemed frantic at the time!), each instalment of which now comes laden with as much suspense and action as seems humanly possible to contain in an hour. 

But there is another factor in the success of the show that has become more and more apparent over the years. A show which is primarily a twenty-four hour action movie is commonly perceived to be weak on character development: if we only get to see one day in the life of the protagonists over the course of a whole season, how are they ever to become anything more than mere ciphers to us, the audience. Well, somehow, the writers (and more importantly, the actors) manage to do it. It's a trick that is particularly important for this show because of the high death rate of leading characters. No other show is as merciless in killing off favourite characters as "24" -- and this season proved even more merciless than the rest — to the point where the viewer couldn't count on anyone (except perhaps Jack Bauer) still being around in the next episode.

The fact that the killing of certain characters provokes such a large response from the fans is proof that 24's protagonists become as real to its audience as do any other show's. Those that stick around for more than one season get to develop, despite the fact that, in real time of the series, we've only known them for a few days; and it's largely down to the actors finding ways to draw out the inner-core of their characters in their responses to the critical threats that they are constantly being asked to face. The biggest example of this is the character Chloe O' Brian (Mary Lynn Rajskub). When the character was first introduced in season 3, she seemed like just another throwaway cipher who was destined to make very little impression; but over the ensuing seasons the character has grown into a firm fan favourite, with every little smidgen of information that one can glean about Chloe's personal life outside CTU, seeming to gain much greater significance in colouring in her personality — largely because details like this are so rare in a series like "24", and partly because Rajskub has been allowed to create such an intriguing, quirky character from such slim, unpromising material.

At the start of Season 5, it is the death of a character who has been around since the very first season that sparks the action and drives it for the remainder of the twenty-four episodes. For the first time, the writers manage to tie everything up perfectly to a catastrophic murder of one of the shows recurring characters, that takes place in the first few minutes of episode One. If you haven't seen the show and don't want to read any spoilers, than stop reading now — its impossible to talk about this Season without giving away a few key facts.

Episode One sees Jack (Kiefer Sutherland) living an ordinary life under an assumed name after faking his death at the end of Season 4, in order to escape detection by the Chinese authorities who wanted him deported on charges of murder. When the ex-president Palmer is assassinated, and two of Jack's closest friends during his time at CTU are blown up in a car bomb, it becomes apparent that someone has discovered that Jack Bauer is still alive and is busy killing everyone who already knew the truth. Jack breaks his anonymity in order to save Chloe but finds himself a hunted man when it becomes apparent that he has been framed for President Palmer's death. Meanwhile, as the current incumbent in the White House, President Logan (Gregory Itzin), prepares to sign an important deal promising co-operation in dealing with terrorists between the U.S. and Russia, Russian extremists take over Los Angeles airport, threatening to release deadly nerve gas if Logan signs the treaty. Before the end of the day, Bauer will have to clear his name, find the canisters of nerve gas, cope with CTU being rendered in-operational when the terrorists release a nerve gas canister into its air vents, face up against his greatest foe yet: the man who recruited him to CTU but who has now gone bad, and uncover a shocking conspiracy in the upper-ranks of the White House administration.

Knowing the bond Jack had with President Palmer (and the other long-standing characters who are killed this season) helps up the stakes and makes this the most fraught series of "24" yet; once again, there is an excellent supporting cast with James Morrison becoming a huge linchpin since the introduction of his character, Bill Buchanan, midway through Season 4; and Kim Raver is also excellent as Jack's love interest Audrey Raines. We get some powerhouse villains this season too: with Peter Weller and Julian Sands turning in memorable guest appearances as some of Jack's most ruthless foes yet. We may have lost President Palmer, but Gregory Itzin creates a very colourful replacement in the form of the slimy Charles Logan (a characterisation that seems part way between Jimmy Stewart and Nixon!). The series ends on a cliff-hanger which, although dramatic, seems to make things very difficult for the start of season six (due in January 2007) but doubtless we are in for an even more explosive season, since the creators have set themselves a very high bar with the relentless high quality of season 5.

The box set comes loaded with the usual array of extras in the form of commentaries, documentaries, featurettes and deleted scenes.