The perp hadn’t used a manhole to gain access. This tunnel, one of three, opened onto a train track – the line running north from Penn Station. The opening was largely obscured by a pile of debris but there was plenty of room for a person to climb over it. The unsub had simply walked up or down the tracks, from a spot near the West Side Highway, and then scaled the rubble and made his way to the octagon-shaped space where Samantha had died. She radioed Jean Eagleston and told her about the secondary crime scene – the entrance/exit route.

Then Sachs returned to the center of the octagon, where the victim lay. She looked up and shielded her eyes from the brilliant halogens the medics had set up. ‘Another flashlight, Rhyme. He sure wants to be certain nobody misses the vic.’

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Like Chloe, Samantha was handcuffed and her ankles duct-taped. She’d also been partially disrobed – but only to expose her abdomen, where the unsub had inked her. A fast examination revealed no apparent sexual contact here either. Indeed, there was something oddly chaste about the way he’d left both victims. This was, she reflected, eerier than a straight-up sex crime – since it suggested the underlying mystery of the case: Why was he doing this? Rape, at least, was categorical. This?

She gazed down at the tattoo.

Rhyme’s voice intruded on the quiet. ‘“forty”. Lowercase again. Part of the phrase. Cardinal number this time, not the ordinal “fortieth”. Why?’ Testily he added, ‘Well, no time to speculate. Let’s get going.’

She processed the body, scraping nails (nothing obvious this time, as with Chloe), taking samples of the blood, the body fluids and presumably the poison oozing from the wounds. Then scanning her for prints, though he’d worn gloves again, of course.

Sachs walked the grid, collecting trace near the body and distant samples of dirt and trace too, for control. She studied the ground. ‘Booties again. No tread marks.’

‘He’s wearing new shoes,’ Rhyme said. ‘He’ll’ve pitched the others, the famous Bass size elevens. They’re in the sewer in the Bronx by now.’

As she walked the grid, she noticed something against one of the far walls. At first she thought it was a rat lying on its side. The lump wasn’t moving so she speculated that the creature chewed a bit of Samantha’s flesh, ingested the poison and crawled away to die.

But as she got closer she noted that, no, it was a purse.

‘Got her handbag.’

‘Good. Maybe there’ll be trace on that.’

She collected it and dropped the leather purse into an evidence bag.

This and all of the other samples of trace, also bagged in plastic or paper, she added to a milk crate.