‘But they know we’re here,’ said Elyas Assadi.

‘Perhaps, but even if they do it is too late for them to do anything,’ said al-Hussain. He put his eye to the scope and focused on the helicopter. When it had first appeared he had assumed it was a random patrol but it had stayed in its present position for almost a minute and it appeared to be concentrating on the building. He could just make out the two figures but he knew there was no point in trying to shoot through the Plexiglas. Even if it wasn’t bulletproof the round would almost certainly ricochet off it. He moved the rifle slightly to the right and took aim just below where the rear tail rotor was spinning. The first shot hit bang on target but didn’t seem to have any effect. The second shot smacked into the tail and a few seconds later black smoke poured out and the rotor started to flicker. The helicopter began to rotate and al-Hussain took his eye away from the scope. Without the tail rotor functioning properly the helicopter was impossible to control and began to spin crazily.

It lost height rapidly, still spinning, and the lower it got, the faster it spun. It disappeared from view and a few seconds later al-Hussain heard the dull thump of an explosion as it hit the ground. His magazine was empty so he ejected it and slotted in a fresh one. He already had the scope to his eye and was selecting his next target as grey smoke plumed up from the wreckage of the helicopter.

Eight doors faced the lifts, each with a number: 1202 to 1216. All even numbers. ‘You should hang back, Jeremy,’ said Shepherd, ‘seeing as how you don’t have a gun.’

Willoughby-Brown nodded. Shepherd was impressed by the man’s calmness. He had seemed perfectly ready to go charging in even though he was unarmed.

Shepherd ran the numbers. The superintendent in Met Control had said fifth window from the left. There had been twenty-four windows running the length of the building, which suggested three per flat. That meant the sniper was in the second flat from the left looking at the building: 1214. Assuming all the flats were the same size. In a perfect world they would have obtained a floor plan of the building but there was no time.

Shepherd pointed for the three armed cops to take up positions either side of the door to flat 1214. There was no time for subterfuge, no time to pretend to be delivering a parcel or checking for a leak: a frontal assault was the only way to go.

‘There’s another one,’ said Chapman. ‘Up in the stands.’

‘A stabbing?’

‘They don’t know. He was in the middle of a row and no one saw anything. But the guy has a wound in his shoulder and is bleeding to death. We need ambulances, now. Lots of them. We’ve got paramedics but we need to get them to hospital.’