Take a bunch of boffins (and a couple of ordinary folk) and put them in their own town in the Pacific Northwest of America, to which access is limited. Cue lots of experiments going comically awry. No, this isn't a variant of Big Brother (although we'd actually really like to see that variant). This is A Town Called Eureka (known simply as Eureka in its native US), a combination of comedy, drama and science fiction that first graced our screens back in 2006. Since then it's won itself an audience in the millions and has been nominated for - and won some - awards for its visual effects. The first half of the fourth season is now available on DVD, but is it worth investing your time and money in?

This season kicks off with Founder's Day, an annual holiday where both the town and its people dress up like it's 1947 in order to - you guessed it - celebrate its Founders. This being Eureka, it's hardly a surprise when some piece of high-tech gadgetry goes haywire: this time it's a piece of kit from the forties, which jettisons Carter (Colin Ferguson), Allison (Salli Richardson-Whitfield), Lupo (Erica Cerra), Fargo (Neil Grayston) and Henry (Joe Morton) back through time to the original Founder's Day. Shenanigans ensue. Eventually they manage to travel 'back to the future' (via the timely intervention of a solar flare, not a lightning strike...) that just happened to coincide with a dance (another echo of BTTF), but they inadvertently bring back one of the founders with them (Trevor Grant, played by James Callis). Through their meddling, the future to which they return is not quite the same as the one they left: Allison's autistic son is autistic no longer; Henry suddenly finds himself married to Grace (Tembi Locke), a veritable stranger; Carter is still very much in a relationship that had previously ended; Lupo is surprised to find that she has never been in a relationship with Zane (Niall Matter), who had just proposed in the alternative timeline; and everyone is surprised to find that Fargo is running Global Dynamics.

This storyline runs throughout the subsequent episodes. Much is made of the impossibility of their telling anyone about what has happened for fear of the repercussions, but that doesn't seem to stop Henry letting on to his new wife.

There's lots of love triangle action going on all over the place in this season. Back in 1947, Carter finally kissed Allison but the new 1947 dude, Dr Grant (winningly nicknamed 'Old Spice' by Carter), also wants a piece of the action. This particular love triangle turns into a bit of a pentagon in one episode, when both Carter's and Allison's exes pop in to complicate things even further. There's also the intriguing Henry-Grace-Henry love triangle, where Grace is still in love with the previous Henry that the current Henry has replaced. Then there's the Lupo-Zane-Zoe love triangle, which is frankly a bit dreary.

Other highlights of this season (or should we say the first half of this season) include killer bee zombies, dematerialising tools, rematerialising bits of 1947, an invisible angry cat, a guest appearance from the brilliant Claudia Donovan (Allison Scagliotti) from Warehouse 13, a surprisingly physical romance between a robotic policeman and S.A.R.A.H. the house, and Henry singing his version of the Thomas Dolby eighties classic, 'She Blinded Me With Science'.

I think they're onto us. Quick, fire up the flux capacitor, take me back to the future!

Although every episode begins with a précis of the timeline narrative with the strapline "Same town, big changes," it's not actually that big a change for Eureka. It's not the first time that the creators of Eureka have attempted to make things more interesting by fiddling about with timelines in the town. Remember back in season one, when a possible future in which Carter and Allison were married and expecting a child was annihilated in order to prevent Henry's wife from dying, which eventually led to a new future in which Allison married her slightly evil ex, Nathan Stark, instead? Still, timeline tinkering is a fairly winning idea, and it works just as well second time around.

It is a bit irritating that the season is split into two parts: we have to wait for the second half, season 4.5, to be released on DVD, to find out what happens after the slight cliffhanger at the end of season 4.0. This savvy marketing strategy was also deployed for the release of season 3, although you can buy seasons 1 and 2 as the complete set. At the moment it's looking as though season 5 might be the last one for Eureka, after which we can no doubt expect to encounter a box set release as yet another cunning way to get Eurekaphiles to hand over the readies.

There's not much in the way of DVD extras, either: just some deleted scenes and an audio commentary.

Even though you know exactly what you're going to get with every episode - some kind of madcap technology-gone-wrong escapades with a heavy dollop of relationships on the side - it works. It's like donning your comfiest PJs. Of course, it's sad that they've messed about with some of the characters over the course of the four series - like the initially gloriously kick-ass Lupo that has ill-advisedly been transformed into a rather wet, simpering and high maintenance girlie girl - but on the whole, their gift for telling some pretty fun and engaging stories means that they can be forgiven. Probably.