‘Hello,’ said the pilot, ‘what’s this?’

He’d spotted another boat, circling the platform at a distance of maybe half a mile.

‘Protesters,’ he said. ‘Bloody idiots.’

Lumsden looked out of his window, pointing. Rebus saw it: a narrow boat painted orange, its sails down. It looked to be very close to the safety ship.

‘They could get themselves killed,’ Lumsden said. ‘And good riddance.’

‘I do like a copper with a balanced view.’

They swept out to sea again and banked sharply, then headed for the heliport. Rebus was deep in prayer as they seemed to weave wildly, only fifty feet or so above the deck. He could see the helipad, then whitecapped water, then the helipad again. And then they were down, landing on what looked like a fishing net, covering the white capital H. The doors opened and Rebus removed his ear-protectors. The last words he heard were, ‘Keep your head down when you get out.’

He kept his head down when he got out. Two men in orange overalls, wearing yellow hard hats and ear-protectors, led them off the helipad and handed out hard hats. The engineers were led one way, Rebus and Lumsden another.

‘You’ll probably want a mug of tea after that,’ their guide said. He saw that Rebus was having trouble with the hat. ‘You can adjust the strap.’ He showed him how. There was a fierce wind blowing, and Rebus said as much. The man laughed.

‘This is dead calm,’ he yelled into the wind.

Rebus felt like he wanted to hang on to something. It wasn’t just the wind, it was the feeling of how fragile this whole enterprise was. He’d expected to see and smell oil, but the most obvious product around here wasn’t oil – it was seawater. The North Sea surrounded him, massive compared to this speck of welded metal. It insinuated itself into his lungs; the salt gusts stung his cheeks. It rose in vast waves as if to engulf him. It seemed bigger than the sky above it, a force as threatening as any in nature. The guide was smiling.

‘I know just what you’re thinking. I thought the same thing myself first time I came out here.’

Rebus nodded. The Nationalists said it was Scotland’s oil, the oil companies had the exploitation rights, but the picture out here told a different story: oil belonged to the sea, and the sea wouldn’t give it up without a fight.

Their guide led them to the relative safety of the canteen. It was clean and quiet, with brick troughs filled with plants, and long white tables ready for the next shift. A couple of orange overalls sat drinking tea at one table, while at another three men in checked shirts ate chocolate bars and yoghurt.

‘This place is mad at mealtimes,’ the guide said, grabbing a tray. ‘Tea all right for you?’

Lumsden and Rebus agreed that tea was fine. There was a long serving-hatch, and a woman at the far end smiling at them.