Chewing the sawdusty slab as the train carried her towards Elephant and Castle, she found herself absentmindedly rubbing her ribs where she had collided with the large man in the goatee. Being sworn at by random people was the price you paid for living in London, of course; she could not ever remember a stranger swearing at her in Masham, not even once.

Something made her suddenly look all around her, but there did not seem to be any large man in her vicinity, neither in the sparsely occupied carriage nor peering at her from the neighboring ones. Now she came to think of it, she had jettisoned some of her habitual vigilance that morning, lulled by the familiarity of Catford Broadway, distracted by her thoughts of Brockbank and Zahara. She wondered whether she would have noticed somebody else there, watching her… but that, surely, was paranoia. Matthew had dropped her off in the Land Rover that morning; how could the killer have followed her to Catford unless he had been waiting in some kind of vehicle at Hastings Road?

Nevertheless, she thought, she must guard against complacency. When she got off the train she noticed a tall dark man walking a little behind her, and deliberately stopped to let him pass. He did not give her a second look. I’m definitely being paranoid, she thought, dropping the unfinished energy bar into a bin.

It was half past one before she reached the forecourt of Wollaston Close, the Strata building looming over the shabby old flats like an emissary from the future. The long sundress and the old denim jacket that had fitted in so well in the market in Catford felt a little studentish here. Yet again pretending to be on her mobile, Robin looked casually upwards and her heart gave a little skip.

Something had changed. The curtains had been pulled back.

Hyperaware now, she maintained her course in case he was looking out of the window, intending to find a place in shadow where she could keep an eye on his balcony. So intent was she on finding the perfect place to lurk, and on maintaining the appearance of a natural conversation, that she had no attention to spare for where she was treading.

“No!” Robin squealed as her right foot skidded out from under her, her left became caught in the hem of her long skirt and she slid into an undignified half-splits before toppling sideways and dropping her mobile.

“Oh bugger,” she moaned. Whatever she had slipped in looked like vomit or even diarrhea: some was clinging to her dress, to her sandal, and she had grazed her hand on landing, but it was the precise identity of the thick, yellow-brown, glutinous lumpy stuff that worried her most.

Somewhere in her vicinity a man burst out laughing. Cross and humiliated, she tried to get up without spreading the muck further over her clothes and shoes and did not look immediately for the source of the jeering noise.