Now Sellitto was frowning. ‘How do you know the decade, Linc?’

‘The typeface. It’s called Myriad. Created by Robert Slimbach and Carol Twombly for Adobe Systems. It became Apple’s font.’

‘It looks like any other sans serif font to me,’ Sachs said.

‘Look at the “y” descender and the slanting “e”.’

‘You studied that?’ asked Pulaski, as if a huge gap in his forensic education threatened to swallow him whole.

Years ago Rhyme had run a kidnapping case in which the perp had crafted a ransom note by cutting letters from a magazine. He’d used characters from editorial headlines as well as from a number of advertisements. Correlating the typefaces from dozens of magazines and advertisers’ logos, Rhyme had concluded it was from a particular issue of the Atlantic Monthly. A warrant for subscriber lists – and some other evidence – led to the perp’s door and the rescue of the victim. He explained this to Pulaski.

‘But how do we date it more specifically?’ Sellitto asked.

‘The ink,’ Rhyme said.

‘Tags?’ Cooper asked.

‘Doubt it.’ In the 1960s ink manufacturers began adding tags – chemical markers, in the same way that explosives manufacturers did – so that, in the event of a crime, the ink sample would be easy to trace to a single source or at least to a brand name of ink or pen. (The primary purpose of tagging was to track down forgers, though the markers also nailed a number of kidnappers and psychopathic killers, who left messages at the scenes of their crimes.) But the ink used for book printing, as in this sample, was sold in large batches, which were rarely if ever tagged.

So, Rhyme explained, they needed to compare the composition of this particular ink with those in the NYPD ink database.

‘Extract the ink, Mel. Let’s find out what it’s made out of.’

From a rack of tools above the evidence examination tables, Cooper selected a modified hypodermic syringe, the point partially filed down. He poked this through the paper seven times. The resulting tiny disks, all of which contained samples of the ink, he soaked in pyridine to extract the ink itself. He dried the solution to a powdery residue, which he then analyzed.

Cooper and Rhyme looked over the resulting chromatogram – a bar chart of peaks and valleys representing the ink used in the printing of the mysterious book.

By itself, the analysis meant nothing, but running the results through the database revealed that the ink was similar to those used in the production of adult trade books from 1996 through 2000.

‘Adult?’ Pulaski asked.

‘No, not your kind of adult books,’ Sellitto said, laughing.

‘My—’ The officer was blushing furiously. ‘Wait.’

Rhyme continued, ‘It means as opposed to juvenile publishing. Legitimate books for adults. And the paper? Check acidity.’

Cooper ran a basic pH analysis, using a small corner of the paper.

‘It’s very acidic.’