If you’re reading this in the Southern Hemisphere — or in the year 2047, when global warming has reduced the planet to a scorched wasteland — then the raft of snow-bound mysteries reviewed in the run-up to Christmas might seem a little odd. Nevertheless, this snowswept tale of impossible murder, which came recommended by Tom Mead, has been reserved for this precise season so that its twofold chills — physical and atmospheric — might be better appreciated. Gerald Verner wrote so much that it would be easy to believe that quality wasn’t high on his agenda, but he does good work in They Walk in Darkness (1947) even if the overall edifice doesn’t quite live up to its promise.