There comes a moment when they both fall silent as her daughter takes a long shuddering breath, and that’s when the memory drops into Caro’s consciousness, perfect as a drop of water off a stalactite. Down it smashes, tiny but insistent, into a little pool of something calcified and secret. ‘I got stung by a wasp when I was about four years old,’ she says to her daughter. ‘It really hurts, doesn’t it?’