The cameras on the drones would relay their pictures back to Abu Mujahid and Saleem’s phones in real time. The explosives would be set off by a separate radio signal using a small relay, built into a box the size of a pack of cards. The two relays had been assembled in Syria and sent to Burgess Hill in the cache of weapons and Semtex. Having two controllers each – one for the drone, the other for the explosive – was clunky, but it was the simplest and most foolproof way.

Abu Mujahid went onto the balcony and stared again at the helicopters. Something was not right. One was not just circling the area, it was staying close to the flat – up one side of the street, around to the kids’ park and back again in a loop.

A coincidence? Unlikely. Had Mirza betrayed them? Again unlikely. The boy was an idiot, not a traitor. Maybe the block was under surveillance. He watched the helicopter for a few seconds longer. If the flat was being watched, then police could be here any second. Change of plan, he thought.

‘Stay here, Waheed,’ he called out. ‘I’m going to check out the street. I’ll find somewhere secure outside and run my drone from there. Move the drones clear of the table in five minutes ready for the launch. Watch your camera feed and detonate at the right moment.’

Saleem looked surprised but said nothing as Abu Mujahid grabbed his phone and one of the grey relay boxes and stepped into the hallway. He opened the cupboard door, reaching behind Mirza’s wrapped body to yank out a motorcycle helmet from the shelf, out of sight of Saleem, then slipped out of the flat’s front door into the communal hallway.

#

CTOC, St Pancras, London

It took five minutes to get the owner’s details from Airbnb.

Bose gave the news to Gabriel. ‘It’s flat seventeen, ma’am, top floor, facing north with a large balcony. It’s currently being rented – for four weeks, starting two weeks ago.’

‘And the host?’ said Gabriel.

‘Turns out to be an estate agent herself. Forty-two, no previous, not on our radar. Has multiple properties and has been with them for three years. Lives in West London. According to Airbnb, she hands over the keys in person to the renter. Do we send someone round to her, ma’am?’

Gabriel hesitated. Normally she’d say yes. This woman could be in on the plot. But there was simply not enough time to be cautious. She would have to gamble. ‘Given her profile – and the fact she’s got a few flats – we’ve got to assume she’s not involved in whatever Abu Mujahid is planning. Get her on the phone ASAP and get a description of the person renting.’

#

‘They’ve spoken to the owner of the flat on the phone, ma’am,’ said Bose. ‘And it’s the right flat. It seems Abu Mujahid booked it initially for a week from overseas, but then asked if he could extend the rental for another three weeks once he’d seen it in person. He came to meet the owner a couple of weeks ago to collect the keys. We texted the owner a picture of Abu Mujahid and she’s ninety per cent sure it’s him.’