Like any desert trip, Lawrence Osborne’s The Forgiven is alarming and liberating in equal measure. Here is a tale as hot, claustrophobic and gritty as being rolled in the sand after a sweat bath. But it’s also a novel with a vast moral horizon, which recedes and advances disorientatingly, leaving the reader with a sense of vertigo. Written with an untimely elegance more 1930s than 2010s, the book proceeds at thriller pace, or at least it would if almost every page didn’t cause you to fixate on a clinical insight into human nature or a snatch of dream-like description. If it were a film, it would be shot in high definition; every grain of sand would show.

In its opening, The Forgiven consciously echoes Paul Bowles’s The Sheltering Sky. Like Bowles’s Port and Kit Moresby before them, David, a heavy-drinking doctor, and Jo, a floundering children’s author, are a middle-aged couple seeking in Morocco temporary respite from their troubled marriage. Their destination is a remote ksar (castle)