It was late when Honor finally pitched up, maybe just after midnight, and the canal was shrouded in that deep lonely dark that, in London, was unique. Nevis had woken to a cry and gone out to discover her mother, four sheets to the wind, fumbling around in the cratch for the hatch keys.

‘Ssshoory to wake you.’

Nevis let her mother in and saw to it that she got down the steps into the saloon safely since whatever she’d drunk had gone to her legs, which wobbled about like a colt’s. Assuming her mother would want to go directly to bed, Nevis directed her towards her room, but Honor wanted to sit up a while and watch the water so Nevis helped her to her armchair in front of the dying embers in the wood burner, laid a blanket over her lap, and went over to the kettle to make her a cup of chamomile tea. By the time she returned with the tea, only a matter of minutes later, Honor was asleep but she woke with a start when Nevis laid a finger on her arm.

‘Let’s get you to bed.’

Her mother peered at her through glassy eyes and Nevis saw her lips open with the beginnings of a smile. Then in a voice still cracked with sleep Honor said, ‘Zoe? Is that you?’

The pain was as shocking as a knife to the heart. Her own mother, at least the only mother she ever knew, mistaking her for a dead woman, the ghost in whose shadow Nevis had always lived, always knowing that not a day went by when Honor didn’t wish for Zoe’s company. Nevis wanted to say, it’s me, the stand-in, the understudy, the placeholder, the body double, the fraud, but no words came. Instead, she watched as reality hit and tears began to spiral down Honor’s cheeks.

‘Nevis, darling, of course it’s you!’

And then the words came out in a rush, tumbling over one another, and Nevis heard herself say, ‘But you wish it wasn’t, don’t you? You’ve always wished it wasn’t.’

Time seemed to stand still. Nevis saw Honor’s eyes widen into dark pools and her shoulders begin to shake and covering her face with her hands, in a voice that seemed to come up from the depths of the canal itself, Honor said, ‘Never, ever say that again,’ and Nevis knew she had gone too far, that she had touched a nerve so tender and raw that to touch it again would break them apart.