Five episodes into the fourth series – and heading towards a mid-season crescendo foisted on it by the writers’ strike – Lost has hit the accelerator. Compared, anyway, to the glacial speed at which it has previously teased out the overarching plot.

Monday’s episode (from RTÉ2 viewers’ perspectives), The Constant featured further confirmation that there’s a big time-travel element involved. I could go into the details of plot links, twists, connections, red herrings, and all that, but it would be at the severe risk of losing whatever non-Lost-watching reader has already got this far in the post.

Lost is not a programme you pick up five episodes into the fourth series. It’s not something that you suddenly decide you’ll sit down to watch, presuming you’ll pick it up along the way.

It has, according to its makers, six series in total, and following its slow reveal of the last season especially, it has finally decided to deliver some answers. Which is where its problems may begin.

While The Constant offered plenty of new clues and a couple of answers, it also came pretty close to being a Star Trek episode. Until now, Lost has survived by being many things – a supernatural mystery, a Lord of the Flies adventure, a horror, a murder thriller, a what-the-hell-will-happen next fun fest. But this episode it was sci-fi. And sci-fi is not to everyone’s taste.

Those who have been sticking with Lost, of course, are unlikely to give up now. Not after all this time. But as it moves towards some sort of revelation – we hope – it faces the problems faced by some of its evolutionary cousins. Twin Peaks bored viewers in its second series. The X-Files was always at its best when it withheld information, and quickly leaked ratings because – among other reasons – it coughed up answers that were far more ridiculous than the questions.

Meanwhile, Heroes contrasted the frustration of Lost by wrapping a hell of a lot of stuff up by the end of the first season.

Lost is still brilliant at times. It has become increasingly playful, throwing in glimpses of the future to replace the flashbacks, while finally moving off the island – even if it is only to a boat offshore. And it is getting somewhere, even if plot holes and loose ends abound.

But its biggest trick will be in keeping the audience happy as it reveals whatever secrets it has. And you don’t need to be “unstuck in time” to predict that viewer disappointment remains the most likely outcome.