Again, the five-second image: a white beach and blue sea, and a lone woman, just about in a bikini, lithe and tanned and happy, running into the waves. Visit Greece, it said.

Mary didn’t have a passport. She didn’t even know if she had the documents to get a passport. She knew she’d need a birth certificate, and if one existed for her, she’d never seen it.

She imagined it, for a moment. That she was the woman. That the white sand was hot under her feet and between her toes. That the water was clear and bright and broke like diamonds as the wave hit her shins.

She stumbled off the end of the escalator, nearly falling in the process.

It was a dream. A pipe-dream. The woman in the jeweller’s would one day meet a rich man who liked her enough to take her on holiday to Greece. And good for her. Nothing wrong in that. If she had the opportunity, she should grasp at it with both hands, and get out while she still could.

Mary took the stairs down to the westbound platform of the Piccadilly line. The last train was still ten minutes away. She was early.

There was nowhere to change. Literally, nowhere. Whatever she was going to do, she had to do it here on the platform, amongst the drunks and the stoners. She could wait, but then it was always a rush to get kitted out, Mr Nicholls with his clipboard chivvying and tapping and looking at his watch.

So she walked down to the far end of the platform, right to where the jumpers usually positioned themselves for their one final step across the ill-minded gap, and dropped her bag to the ground.

The CCTV could see her, so she turned her back as she shucked her jacket. All she was wearing underneath was a thin tan vest that was a shade lighter than her skin. It got hot, working in the tunnels, and the first day, against all advice, she’d made the mistake of wearing a T-shirt and a pair of sweat pants.

She’d cooked, and she wasn’t going to do that again.

From inside her bag, she dragged her thick orange boilersuit. Ironically, it made her look like she was on a chain gang, or she was one of those Guantanamo inmates. She shook it out, kicked off her shoes, and quickly dragged her jeans down to her ankles.

The rumbling she felt through her feet told her that a train was due. Probably eastbound on Piccadilly, as it was too solid a hit to be the nearby Northern line.

Someone wolf-whistled. She ignored them, and sat on the platform, on the boiler suit, to pull her jeans free.