‘It’ll be fun,’ she had suggested brightly, some weeks back. ‘It’s a marathon performance of Wagner’s Parsifal at the Royal Opera House. We can go halfsies on a box with Richard and Sarah and I’ll smuggle us in a bottle of champagne and some of those Belgian chocolate truffles you like. Go on, say yes!’

The evening had turned out to be anything but fun. It had got off to a bad start when Luke had turned up hopelessly late, having driven straight from the Killing House on the Welsh borders and then taken ages trying to find somewhere to park. He had kept Elise waiting, alone, nursing a drink at the crowded bar, being bothered by a ruddy-faced man with cigar breath. When he did finally show up, profusely apologetic, they had only just made it to their seats before the curtain went up. Their friends Richard and Sarah had blown them out at the last minute when their babysitter had called in sick. So now here they were, sitting in brooding silence in their half-empty box with two vacant red velvet chairs beside them, the opened bottle of Moët on the floor between them, barely touched. It was as if the gloom of this late-nineteenth-century German opera had somehow managed to wrap itself around the pair of them.

And it was not as if their relationship was exactly firing on all cylinders. More than a year had passed since Luke had returned from a lengthy agent-running op in Iran. The mission had been hailed in Whitehall as a triumph: a kidnapped British minister freed from a remote Gulf island in a daring hostage-rescue operation. Luke and the Service had played a major role in locating him and he had returned to SIS headquarters at Vauxhall Cross to a hero’s welcome. But in Elise’s and his shared flat in Battersea he had met a somewhat less enthusiastic reception. While Luke had been in Iran and out of contact for days on end, Elise’s mother had lost her battle with liver cancer. He had managed to miss the funeral, and for that he had still not been forgiven. When he had finally returned, limbs still aching and the exhaustion showing in the bags beneath his eyes, he had found Elise cold and withdrawn. His absence during the funeral had been unforgivable, she’d told him. She couldn’t help looking at him differently now, she said, and it would take her a long time to get over this.

So there was that, and then there was the other matter of something that had happened while he was in Iran. Something he wasn’t proud of at all. Something he hadn’t yet decided whether to tell her about. For now, he had parcelled it away in a box in his head and called it ‘The Secret’. But sooner or later, Luke knew, he was going to have to do something about it.