Britain is gripped by its coldest winter in years. Blizzards sweep the country, trapping elderly detectives Bryant and May - en route to a spiritualists' convention - somewhere on Dartmoor. Not the place to be when, back at the Peculiar Crimes Unit HQ in London, one of the team has been found dead in highly suspect circumstances.

But as the snow thickens and temperatures plummet, things are about to get much, much worse for the two octogenarian policemen. For along the line of vehicles stranded on this desolate stretch of road prowls a killer - a deranged murderer who is edging ever closer to one particular victim.

With no official help at hand and armed only with their wits, woolly coats and a mobile phone with a fading battery, can Bryant and May solve two very different crimes in time to prevent the pristine snow being stained blood red?