What sets The Wayward Girls apart is its finesse. With a touch so light that it appears accidental at first, Mason arranges things in pairs. Two girls look alike; one character is called Loo, and another Lew; there are two sets of researchers, and two haunted houses – one occupied by a young family, the other a care home. Before long, these pairs start to feel like the flickering of two images pasted together on a film reel. Even the prose has a celluloid quality; the point of view switches mid-paragraph so suddenly that it can be hard to follow, as though the film on the projector has slipped. Brilliantly, all of that is a clue.