They looked at each other, standing outside in the sunlight, and Ross felt the weight of how long she’d been awake, the need for more meth to keep her going. They’d kept working through the night to try and find Jimmy, then to go and see his body. On the way here, the Data Protection Act results had come back, forwarded from the main inquiry, concerning the tweets that led to the mob outside the bar and the later ones that had sparked off the crowds of Toffs near Quill. All of the Twitter accounts, and there were several involved, had been set up by anonymous webmail users whose chosen names looked to be deliberately random strings of letters and numbers. The contact details given were plausible-sounding street names, but uniformly fictional; the phone numbers all led to the monotone of unreal connections. Ross had Googled the words but could find no connection between them, except that some of them were actual streets in a random scatter of different towns.

Without saying anything, she marched back into the Portakabin; the other two followed. She went to the Ops Board. ‘Adding the two big questions,’ she said, picking up a marker, feeling numb and roaring at the same time. ‘One: why did the Ripper kill Quill?’ She wrote ‘motive?’ beside a victim line connecting Quill to the Ripper.

‘It must be something we learned recently,’ said Costain, ‘between the last murder and now.’ He paced back and forth. ‘It must be. It must be.’

‘Mary Arthur,’ said Sefton, pointing to the CCTV camera still of her. ‘Jimmy was sure we were onto something with her. She has a possible link to Spatley. Somehow she’s the only survivor of an attack by the Ripper—’

‘Ironic,’ said Ross, ‘her being a prostitute.’ Then she chided herself. The choice that was looming over her was putting her off her game. She was letting Jimmy down. ‘No, fuck “ironic”, significant. Potentially.’

‘She’s the lead we’ve recently been pursuing. Fruitlessly, so far, because that bar is the only place she’s been seen since she vanished.’

‘She might have needed funds, decided to turn a trick again,’ said Sefton.

‘Hoxton nick hasn’t laid eyes on her, despite the description doing the rounds,’ said Costain.

‘It’s the same pattern,’ said Ross, ‘as with Tunstall’s death: we discover something new, someone who can follow up on that is murdered. Now, question two: how did the Ripper locate Quill?’ Ross wrote ‘how?’ beside the same line, and underlined it many times.

‘I want a watch on Twitter,’ said Costain. ‘If anyone tries to start a flash mob of those Toff fuckers anywhere near us, I want some warning. I want to know, okay?’

‘Already on it,’ said Sefton.