Now he heard again the noise that had woken him, which in his dream he had interpreted as the breaking of an icy Arctic crust. It was something at the back door. Leaping from the bed, knife in hand, he opened the bedroom’s casement window which looked down over the back door.

Of course. Trish’s bloody cats. Not fed for a day or so, and now trying to get into his home through the cat flap which he had glued up months ago. Napoleon, the green-eyed ginger tom and leader of this feral brood, cried up at him. No human can quite match the sense of entitlement of a cat.

He suspected he would get no sleep now.

Seven a.m. on a cool Saturday morning in April found DI John Perry sitting at his desk at Mount Browne, looking at all the DNA tests that had been ordered for both the Ulbricht and Morris murders. The vast majority of positive results were elimination samples, where a CSI technician or a police officer had left traces on evidence. DC Hoskins, for example, had managed to leave a DNA sample on Beatrice Ulbricht’s multi-coloured scarf. Gillard had left his traces on the inside of the evidence envelope in which Beatrice’s hair had been found. Perry himself had left a trace on the cardigan which had been found on Jane Morris’ body. Unfortunately the tiny amount of blood trapped under the fingernail of the middle finger of Beatrice Ulbricht’s left hand had been too degraded by contact with water to yield a reliable DNA sample.

What he really needed was to find the location where Beatrice had been strangled: a house, a bed, even a car seat. A genuine crime scene where there was a good chance of the attacker having left his DNA. They already knew that it could not be Adrian Singer’s house. Neither his DNA nor hers had been found anywhere that did not match the story he had told. The gap in Beatrice’s life between her disappearance late on Sunday and her failure to arrive at the concert on Tuesday night was like a yawning chasm in the evidence record. After mulling all this over for half an hour, Perry turned his attention to Jane Morris. For all the fact that this was a very cold case indeed, the line of inquiry seemed more straightforward. He went to the forensic lab and asked the male technician to fetch one of the six DNA samples taken from Morris by Dr Delahaye.

‘What kind of test are you after?’

‘Familial,’ Perry replied. ‘I want to find out if anyone whose DNA we have in any of these linked enquiries is related to her.’

‘Okay. We’ll be lucky to get that back by Monday,’ the technician said.

Perry returned to his own desk, and once again flicked through the hundreds of microfiche documents he had photoed and copied onto his datasticks, hoping for some kind of inspiration. There was one very short witness statement from someone called Betty Garrison. It wasn’t a name he had heard before, and the statement merely said that she hadn’t seen her granddaughter Jane for five days before she disappeared. Ah! Betty was the missing girl’s grandmother. The statement gave her date of birth as 9 December 1918. The chances were that she was no longer alive. Still, worth checking out.