The Weekend's Television: Harper's Island, Sun, BBC3 Last Chance To See, Sun, BBC2

Life's a beach, then you die

How much guilt do you like with your pleasure? Or rather how much guilt can you swallow? It's always a tricky bit of mathematics this, trying to avoid that moment at which the eager consumption of something you know to be bad for you tips over into nauseated surfeit.

Sadly, Harper's Island – BBC3's buy-in murder mystery – introduces you to it before the first episode is over. There is one thing to be said in its favour, though, before we get on to all the things that can't. It promises to deliver within just 13 episodes, so you can always treat it like one of those mini packs of Pringles. Even if your willpower collapses the damage is going to be end-stopped. This isn't going to be Lost all over again; a cruel long con in which the fraudster keeps promising you that the pay-off is just around the corner. By the final episode of Harper's Island, you'll know whodunnit, and you can sheepishly dust the crumbs off your clothes and promise yourself that you're never going to be such a pig again.

Harper's Island knows perfectly well that it's junk food. An elimination murder mystery, in which the members of a wedding party get bumped off one by one in a variety of baroque ways, each episode has an onomatopoeic title referring to the sound of the principal death. In last night's double bill, we got "Whap" and "Crackle", which I take it were references to the bisection of one victim and the immolation of another. It isn't always easy to tell though, because the death rate is astounding. Even before the wedding party had set off for the destination, one poor sap had been decapitated, having been lashed to the propellor shaft of the ferry they were travelling on. The location for the wedding party, incidentally, is the site of a notorious serial-killing spree seven years earlier (good choice guys), which means that grisly flashbacks can be tipped into the mix whenever the producers feel that the level of Guignol is dropping dangerously low.

Essentially, it's Agatha Christie's "Ten Little Barbie Dolls", as a clutch of willowy young things, and their Kens, are iced one by one. As for the killer, there are more red herrings around than in an Amsterdam fish market, with bad hats and old feuds and rustling in the shrubbery nudging your suspicions this way and that. There's an evilly precocious child called Madison, who whiles away her downtime burning snails with a magnifying glass, a tattooed emo depressive called JD and sundry surly young men with fish-gutting knives and a grudge. Every now and then, one of the Barbies has a hissy fit and strides away into the woods in her Victoria's Secret lingerie, so that the camera can stalk her voyeuristically through the bushes and she can be spooked by someone harmless popping up from out of frame. It could be great fun, but for the fact that it's all flesh and no bones. By my count, the death toll – on a very small island – is already up to six, and nobody really seems to have noticed that they might have a problem, even though some of the party guests have found themselves spending half a day strung upside down in a mantrap. And though you don't have to really care about the fate of the characters to enjoy a horror movie, you surely need some vague feeling that they care. My suspicion is that the killer is a disgruntled B-movie director, crazed by his failure to make it big in Hollywood, and determined to show the world that he can out-gross the best of them. British viewers may like to know that the prospective slaughterees include a comically ineffectual Englishman, though I rather fear that he's going to be kept around to be teased until the very end.

Stephen Fry cannily does his own mocking, thus ensuring that nobody else gets a word in. In Last Chance To See, he's roaming the globe looking at endangered species. He's qualified for the gig not only because he's the current incumbent of the Palin Chair of Expensive Foreign Travel but also because he house-sat for the writer Douglas Adams when he first made this trip 20 years ago. It's a lot more fun than Harper's Island, taking Fry several hundred miles outside his comfort zone, to areas of the globe that have no reliable IT infrastructure (he looked as if a tarantula had just crawled across his midriff when it dawned on him that he wasn't going to be able to recharge his laptop on an Amazonian river boat). This week, he was trying to find the manatee – an over-upholstered kind of seal that looks startlingly like Stephen Fry in a wetsuit – and he ended up endangering himself, breaking his arm badly during filming. There are worse things than no bars on your mobile phone.