Thrupp held Harper’s upper arm and said, “Don’t even think about it,” but she shoved him out of the way and dived off the high wall, bracing herself because the water was low and she had no idea how deep it might be, or what obstacles she might encounter. The church tower could be plainly seen, but there could have been other buildings under there for all she knew, or unrecovered vehicles that had fallen in, or high levels of silt in which she might become stuck. As she dived she caught sight of a sign sticking out of the water on her right, black lettering on a yellow background: Danger of death: do not jump from the bridge.

Half-expecting to hit something, she entered the water cleanly and was relieved to encounter only a few streaming weeds which caught on her head and arms. The arc of the dive took her under and up again to the surface, where without losing pace she began a front-crawl sprint towards Lauren.

Every third stroke she breathed and checked where Lauren was, whether there was anyone on the shore, ready to stop her. Every third stroke, Lauren was further into the water, and alone. The distance between them closed agonisingly slowly.

More than halfway across the reservoir, she couldn’t hear Thrupp shouting at her anymore because the approaching helicopter had drowned him out. The noise became deafening and she realised it was hovering over her, dipping dangerously low, the pressure from the blades slowing her progress, pushing her under. A rope ladder dropped down in front of her and she swam right past it, but they followed. Glancing towards the shore, she saw that Lauren was waist-deep now.

“Get on the ladder,” commanded the loudspeaker.

“No,” she shouted, though there was no way they would hear her. “Get back. Get away. I’m fine.” She gestured with jabbing hands. When they finally got the message and it lifted, she started out again, but her arms were beginning to tire.

Up ahead, only Lauren’s head was visible. The babies were under.

“No, Lauren, don’t,” she shouted, but then she couldn’t see her anymore, only ripples where she’d gone down and disappeared, concentric circles gradually growing and fading away.