The silence and emptiness of the place were total and eerie. Almost every square foot of its smooth, curved wall tiling was covered in the work of the street artists who’d been venturing down here for decades to use it as a giant canvas. Some of the graffiti must have been thirty years old, undisturbed all this time. Older by far were the ancient advertising billboards from the 1930s and 40s, featuring slogans for products that had ceased to exist long before Ben was born, half-hidden beneath layers of dirt and cobwebs. It was like stepping back into the past. A deserted, dusty old museum. Or a tomb, haunted by the spirits of this strange subterranean world that the city dwellers above had mostly forgotten even existed. Ben wasn’t superstitious but felt a shivery tingle up and down his spine.

‘Oh man,’ Roth said, impressed. ‘You could shoot the most awesome zombie movie down here.’

‘We’re not here for zombies,’ Ben said. He nudged Jafari with his gun. ‘Hurry.’

‘We need to go along the tunnel,’ Jafari said. ‘There are two stations, joined together. The woman is being held in a room near the second station.’

‘Deeper into the deathtrap we go,’ Roth muttered. He had his weapon at the ready, finger hovering close to the trigger. Jafari led them along the deserted platform and into the mouth of the next tunnel section. Dirt and debris littered the tracks. The smell of rats and mould was strong.

The second station was more extensive than the first, with broad stairways leading to different levels and corridors branching off here and there. Fewer urban explorers had ever ventured this far, judging by the lack of street art on the walls. They passed down some steps, heading deeper below ground. Then Jafari pushed through a personnel-only doorway marked ENTRÉE INTERDITE SANS AUTORISATION and led them down a tight, winding service passageway with big duct pipes overhead and more doors left and right.

Ben’s tension was rising with every yard they progressed. He had a relaxed grip on his weapon, but every nerve of his being was alert and primed for instant action, and he sensed the same edginess coming from Roth. They were right in the heart of the labyrinthine complex that the terrorists had made their underground burrow. Anything could happen, at any moment.

Then it did.

Ben heard it first, and swung his MP5 towards the sound a fraction of a second before Roth did the same. Voices and footsteps, approaching from behind a closed steel door to their right. They were suddenly no longer alone down here.

The wall light above had a bad connection and was flickering like a strobe, creating a stop-motion effect. Ben grabbed Jafari’s arm and stepped quickly to the hinge side of the doorway. Roth retreated into the shadows on the other side.