She had found some unique trace in the specimens room, identified by the chromatograph/spectrometer as dimethicone, which was used in cosmetics and industrial lubricants and processed foods to prevent caking. Interestingly it was also the primary ingredient in Silly Putty. Rhyme didn’t dismiss this fact immediately but after some consideration decided that the novelty toy didn’t figure in the unsub’s plan.

‘I think he picked dimethicone up when he grabbed Mrs Stanton.’ Sachs explained that, as a woman in her fifties, she had worn a fair amount of makeup. Sachs dug out her mobile and called the number Harriet had given her. She answered and, after Sachs gave her an update of the case, got the brand name of the woman’s preferred makeup products. Running the manufacturer’s website, Sachs learned that dimethicone was in fact one of the ingredients in her foundation.

Dead end there.

And no other trace or fibers.

As she wrote the details up on the whiteboard chart Sachs said, ‘One other thing. I saw he had a tattoo on his—’ She frowned. ‘Yes, his left arm. An animal or some kind of creature. Maybe a dragon. From that thriller book. The Dragon Tattoo. In red.’

‘Right,’ Sellitto added, looking at his notebook. ‘Harriet Stanton said he had one. She didn’t see what it was, though.’

‘Any trace of the poison he intended to use on the vic?’ Pulaski asked Cooper.

‘Nothing. No toxins on anything that Amelia collected.’

‘I think we can assume he keeps his love potions sealed up until he’s ready to start using them.’ Rhyme was wondering again: Why that MO? Poison was a rare murder weapon now. The technique of killing with toxins, popular through the ages, began to fall out of fashion long ago, in the mid-1800s, after the famed English chemist James Marsh invented a test that could detect arsenic in tissue postmortem. Tests for other toxins soon followed. Homicidal husbands and greedy heirs, who’d believed that doctors would rule cause of death coronary or stroke or illness, began ending up in prison or on the gallows after early forensic detectives presented their cases in court.

Some substances like ethylene glycol – automotive coolant – were still fed to husbands by unhappy wives, and Homeland Security worried about all sorts of toxins as terrorist weapons, ranging from castor beans turned into ricin, to cyanide, to botulinum, which was the deadliest substance in existence (a very mild form of which was used in cosmetic Botox injections); a few kilograms of botulinum could kill every person on earth.

Yet poisons were cumbersome and detectable and hard to administer, not to mention potentially lethal to the poisoners. Why do you love them so much? Rhyme silently asked the unsub.

Mel Cooper interrupted his musings. ‘It was a close call at the hospital. Do you think he’ll go away?’

Rhyme grunted.

‘That means no?’

Sachs interpreted. ‘That means no.’