Lost: Season 5 (2009)

Spoilers for Lost: Season 5 ("Jughead")

It's best to consider Lost as the most demanding – yet rewarding – jigsaw puzzle you have ever tackled. Its story is a rich, growing tapestry of flashbacks, flashforwards and flashes in time that are slowly piecing together to form a beautiful, detailed image. It's a slow, often frustrating process, but when that piece you've been agonising over for so long finally slots into place, the reward is a giddy, euphoric feeling.

Three episodes into its penultimate season and Lost has made finally made the leap into fully-blown science fiction territory, adding another dimension to its already complex narrative. So imagine that lovely flat jigsaw you've been working on is actually one of those funky 3D puzzles.

Casual fans may turn their noses up at this season's principal theme of time travel, but from the moment that thunderous monster began tearing up large patches of jungle in the pilot episode, Lost was showing its sci-fi hand. Its current state is the result of a very natural progression.

While last season's phenomenal Desmond-centric episode, "The Constant" proved that time travel exists in the Lost universe, the fifth season has taken that idea and ran with it. It's a bold move, but the show has danced around the notion for so long that it was an inevitable development.

"Because You Left", this year's season-opener, plunged viewers headfirst into a four-year-long mystery and made no apologies for doing so. If you'd never seen Lost before, lost is precisely what you'd have been. But if you have watched Lost, and watched it devotedly, it was a brilliant continuation of all the themes and characters that have made the show such compulsive viewing.

The second episode, Hurley-centric "The Lie", slowed things down a touch; the cursed lottery winner has always been one of the most relatable characters on the show. It also featured a great expanded role for Hurley's father, played by Cheech Marin. Meanwhile, "Jughead", episode number three, continued the show's run of virtually flawless Desmond episodes. Oh, and I'd like to note that eccentric scientist Daniel Faraday, who I initially felt was overplayed by Jeremy Davies, is developing into one of the most intriguing characters on the show.

Lost has always been an ensemble programme, and that's never been truer than in the fifth season. After just three episodes, there's already been a list of returning guest stars long enough to bewilder anyone but the most ardent of fans. However, as that's precisely what I am, it's thrilling telly. If you struggle to keep up with who's who among the regular cast, good luck remembering returning characters like Ms Hawking, the enigmatic antique saleswoman who convinced Desmond that travelling to the island and pushing the button was his destiny (gibberish to non-fans) in an episode two years back.

If that wasn't enough, this season's new storytelling format that sees the remaining castaways visiting the island at various points in its past really requires viewers to brush up on Lost history (Lostory?). However, that's all part of the fun of unravelling the show's labyrinthine plot. With the island constantly shifting in time, the producers have given themselves the broadest canvas imaginable for exploring the island's past – and future.

Lost has long since become impenetrable for new viewers hoping to make heads or tails of its intricate plot, but that's precisely what makes it such a rewarding viewing experience. Pick up the DVD box sets and get stuck into it. And if you're really struggling with the Lost jigsaw, consider Lostpedia – a wiki entirely devoted to the television series – as the puzzle box from which you can cheat.