‘One final question. Robinson is your married name? What is your brother’s name?’

‘Peters. His name is Ben Peters.’

*

The air is damp and cold and an eerie quiet resonates in Ben Peters’ basement flat in Clapham. Archer and Quinn pull on their blue disposable gloves and enter the living room-cum-kitchen. The interior is unfussy, tidy and modern with no signs of a struggle or a break-in.

Archer stands at the kitchen window where the mask appeared, looks back into the room and on a corner bookshelf, sees it.

‘There,’ she says.

Quinn follows her gaze.

Secreted among a row of paperback novels is a home security camera.

‘This is the sort of camera that records motion and sends it to your phone,’ says Quinn.

He slides away the books from either side and lifts the camera out. ‘It’s disconnected from the mains, which means there may not be a video archive. Those films will be stored in the cloud anyway, not on this device, which makes it next to useless.’

‘Bag it anyway. We’ll take it in for quick fingerprint turnaround.’

‘Do you think our killer has Ben Peters?’

‘I hope not.’

Archer flicks a switch by the kitchen door, lighting up a small yard at the rear. She unlocks the back door and steps outside. The space is around ten-by-ten with a small patio table, two rickety chairs, a rubbish bin and steps leading up to a wooden gate. There is a sliding bolt lock on the gate, but no padlock. Archer takes her torch, leans in for a closer look and shines the beam on the bolt, which is easily accessible from the other side for someone who is tall enough. She notices dent marks on the steel.

‘There was a padlock and it’s been forced,’ says Quinn.

‘It would seem so.’

‘I’ll get Forensics in to comb this place.’

He takes out his smartphone and photographs the damaged bolt.

A notification, containing a Tinder dating app banner notification, pops up on his screen.

Quinn slides the banner away. ‘Excuse me,’ he says.

‘Mr Popular,’ says Archer, with a wry smile.

‘To date, ma’am, all it does is provide a shallow promise of a better life.’

‘I see.’

‘Nothing more.’

She retreats down the steps.

‘Probably best not to tell Lucy Robinson about our assumptions on her brother.’

‘Of course.’

*

Back at the station, Archer is finishing up a call with Grandad, who has just eaten an awful hospital dinner of gristly meat and mashed potatoes. The conversation turns to Jamie, and to her amusement he keeps asking after him as if he is a long-lost friend. She hears a nurse interrupt their conversation.

‘Got to go. Time to sleep apparently. It’s barely seven o’clock!’

Archer smiles. ‘Bye, Grandad. Sleep tight.’

‘Bye, my girl.’