Last Night's TV: Agatha Christie's Marple/ITV1<br />Wonderland &ndash; The Kids Who Play with Fire/BBC2<br />Fisherman's Friends/ITV1

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I don't know whether you care why they didn't ask Evans or not, but if you're hoping for clarification here I'm afraid I'm going to have to disappoint you. I didn't know the answer before I watched Agatha Christie's Marple, never having read that particular novel, and I'm no wiser now that I have. I can tell you who Evans was, because he was played by Mark Williams, who could read out the fine print on a phone contract and make it interesting. Or at least I can tell you who one Evans was, because I was vaguely aware – through the light coma of the final explanation scene – that another Evans was sprung on us at the final moment. But I'm afraid I don't know what they should have asked Evans or why exactly this question was connected to the dying man who'd croaked it out two achingly long hours earlier. I fought sleep valiantly, I promise you, but there were a couple of moments when it had me pinned for a while.

Patrick Barlow did the adaptation, obligingly crowbarring Miss Marple into a plot that didn't have room for her and that showed obvious signs of strain, like an overstuffed suitcase threatening to burst its latches. In Julia McKenzie's oversweetened performance, she came across like a weird lavender-scented stalker, not a fatally underestimated presence in the corner of the drawing room but a manipulative obsessive who simply won't mind her own business. Her intuitions didn't seem all that impressive either: "Can't quite put my finger on it... but something's not right," she said at one point. Could it be the distracted madwoman running around the lawn at night, Miss Marple? Or the fact that everyone in Castle Savage is looking daggers at each other in a way that wouldn't escape the attention of a pre-schooler?

I know, of course, that we're not meant to take this kind of Scooby-Doo plotting seriously. And Barlow obviously meant some lines to be delivered tongue-in-cheek. "His son wanted me to look at his viper," one of the young women said at one point, with an insinuating lilt that Christie herself might not have approved of. And Williams had fun as the jungle botanist who talks of his orchids as "my darling children". But probably nothing short of a full-bore parody could have made the mechanism of the plot bearable, as it creaked slowly through its arbitrary and ludicrous revelations. They keep making the damn things – so I assume someone must enjoy them – but I wish all that talent could be applied to more original ends.

Wonderland – The Kids Who Play with Fire involved the far more nuanced mysteries of real human psychology, looking at three troubled children who'd found themselves referred to a Fire Service specialist unit dealing with firebugs. None of the three children here were full-blown arsonists. They just liked scorching things and were dangerously over-confident about their ability to stop a minor blaze from getting out of hand. "Other people drink and smoke and I just set fire to things," said Hulya defensively – a 14-year-old girl whose rows with her mother were almost invariably followed by a smell of burning. Liam, on the other hand, was inclined to burn holes in his mattress when he got stressed, which, judging from its condition, happened quite frequently. Both of them went for interviews with a therapist so sweetly condescending in her manner that I'd have wanted to set fire to her desk myself, just to get the expression of practised empathy off her face. But whatever she did seemed to work. Hulya's mother was coaxed into giving her daughter the occasional hug, and Liam got to spend a bit of quality time with his mum. In both cases, the rekindled flame of family affection seemed to make other kinds of conflagration unnecessary. Ryan – an Ilfracombe teenager with a mouth like a flame-thrower – was a tougher job but even he appeared to be coming round in the end, after his mother started taking parenting classes. That's where the combustion starts, it seems, whoever strikes the match in the end.

Fisherman's Friends, a documentary about a group of Port Isaac sea-shanty singers who were signed up for a record deal, was very nearly undone by the cosy voiceover, narrated by one of the singers themselves. But – inside the life-affirming clichés about close-knit communities and the joys of friendship – there was an intriguing tale here, about what happens when an amateur pleasure becomes a professional obligation. Having previously only sung on the beach for fun, fuelled by beer, the group suddenly found themselves rising early to appear on breakfast television and doing live performances at one o'clock in the morning on the QVC channel (they were sceptical, but shifted 3,500 units of their CD). Unfortunately, they all still had day job, and when the Cornish tourist season kicked in, juggling their singing commitments with running their businesses became almost impossible. They had also been subjected to a Spinal Tap booking at the Newquay Boardmasters festival, where they performed to a thin scattering of baffled-looking teenagers who were waiting around for the pop acts to come on. I'd have loved to hear what they actually said about that backstage, but instead we got an upbeat bromide about learning to take the rough with the smooth, and a segue into what looked suspiciously like a music-video treatment of one of their songs. It hovered close to advertorial at times, but they made a nice noise if you like your folk music salty.