The third bump woke him. He had become so used to the motions of the train that this extra, unexpected jolt triggered the alarm system in his policeman’s brain, and his eyes flickered open. The first thing he saw was her shoulder blade. It was the colour of white marble, and her skin was impossibly smooth. She had a tiny little birthmark, shaped like a crescent moon, on the tip of her shoulder; at first, he thought it was a tattoo, but when he looked more closely, he could see that it was definitely a slight change in the pigment of her skin. No human-made needle could be so precise.
On the second night that they slept together, the birthmark became a full moon, a perfect circle, light brown and a good inch further away from the tip of her shoulder blade. On their third night together, he
