I’d never met Liam’s sister Isobel, but I knew a few things about her. Sometimes I’d withheld sex until Liam agreed to talk to me for a while first, like in a normal relationship. ‘What do you want me to say?’ Liam would ask, and a few times I suggested he tell me things about his sister. So I knew that in the top year of primary school, Isobel had once copied another pupil’s answers in a Maths test, then burst into tears and confessed all to her parents as soon as she got home that afternoon. She’d cheated successfully and got an excellent mark, but couldn’t enjoy it because of the guilt she felt. Her parents and Liam had advised her that she’d be fine as long as she never cheated again, but Isobel insisted on handing herself in to her Maths teacher, who was far less horrified by the transgression than Isobel herself was.

Liam once told me, trying to prove that women create unnecessary work for themselves and for men, ‘My sister’s revision plans for her GCSEs – not her essays or her coursework, just the plans for the work she intended to do – took up more sheets of paper than every essay I wrote in all my exams put together.’

At the age of fifteen, Isobel announced on New Year’s Eve that she’d given up making New Year’s resolutions and would never make another one as long as she lived. She felt too guilty when she didn’t stick to them, Liam said.

Does this sound like a serial killer to you? Is that someone who’s going to imagine she can get away with killing four innocent people? (I’m afraid I can’t bring myself to think of Marion as innocent.) Is it someone who would want to?

Murderous sociopaths are supposed to spend their childhoods torturing animals and setting fire to buildings, aren’t they? Not learning the flute as Isobel Sturridge did; carrying their instruments around in shiny black cases, diligently practising every night and then sticking their grade certificates up on their bedroom walls with Blu Tack.

The overlap between conscientious flautists and serial killers must be minimal to nonexistent. That’s what I’d have said if Charlie had put me in the picture at that point. There’s simply no way that Isobel Sturridge could be Billy, I’d have told her.

Chapter 17

17

16/1/2015

Simon couldn’t help it: he was excited to be in a room with Isobel Sturridge. He was making a special effort to appear subdued so that Sam, also present, wouldn’t guess how big a deal this was for him. He’d always found it excruciating, the idea that others might observe him caring passionately about something.

For Simon, Isobel Sturridge was a first; noticeably different from all the others.