When Griff Rhys Jones, Rory McGrath and Dara O Briain first recreated the Jerome K Jerome classic Three Men in a Boat four years ago, the show was quite entertaining. I'm not too sure Dame Agatha would be too thrilled though. A show where audiences can doze off for half an hour after one too many brandies and wake up in the knowledge that they haven't missed a thing.

Rather it's unthreatening filler for the Christmas schedules. Perhaps Marple isn't intended to be good drama. Most of them had given few signs of being awake either, with Edward Fox to the fore with his standard-issue, one-size-fits-all aristo performance. There was no way anyone could have worked out anything so intricately absurd given the clues on offer – there wasn't even the remains of a firework in sight – but none of the rest of the cast batted an eyelid.

She sprang to life in the last 10 minutes to deliver the astonishing explanation that the gunshot was not a gunshot but a firework, and that the Marquis of Caterham had both hidden the diamond and accidentally killed the maid 23 years earlier while she was trying to stop him discovering that his wife, who was now dead, had been having an affair with a bloke in an orchestra who now turned out to be the Austrian count who was actually the real father of the marquis's daughter, Virginia. In Julia McKenzie, we have a Marple who gives few signs of consciousness. The original Marple books weren't that demanding, but they had rather more bite than this. It's as if everyone involved with the series has lost confidence in the brand and reckons all the punters will stomach now is some whimsy Christie pastiche.

The secret at chimneys