I got my mobile out. Ben had 389 friends on Facebook, and I started scrolling through his newsfeed, looking for any comments or updates from the last week that might give me a clue as to his whereabouts. But there was nothing to suggest that he had not been in London, albeit keeping a lower profile than usual. We had a couple of dozen Facebook friends in common, but most of his were not familiar to me. So I sent friend requests to the twenty or so people who regularly left comments in Ben’s feed. Some would ignore me, some would delete the request. But others who were less discerning – who just wanted to boost their virtual popularity – would accept, and then I could start going through their profiles too, looking for that one nugget of information that would help me put an end to Ben’s campaign.

Mel commented quite regularly on his Facebook posts, but nothing that would have aroused suspicion. A scroll down her timeline yielded pictures of William, selfies of Mel, pictures of the two of them together. A summer garden party at the Delaneys’ house. Ben tending a huge gas barbecue, a Scotch and soda in his hand, a knowing smile on his face. An album of holiday pictures from Crete this summer. Mel on a girls’ night out with her colleagues from work. Multi-coloured cocktails lined up on a bar.

A picture from March – more than six months ago – made me stop and scroll back. A flash of recognition. Mel had shared a link to a gallery of pictures posted to celebrate twenty years since her GCSEs, entitled: ‘Good times at Claremont Comprehensive’. The title image was from some sort of drama production, a line-up of teenagers in medieval dress, swords and gowns to go with their nineties haircuts. Four men – or, rather, sixteen-year-old boys – and four young women, arm-in-arm, full of smiles, receiving the applause of the audience at the end of a show.

The picture was familiar, but not from March. Much more recently. It was one of the pictures that Beth and Ben had on the wall of their lounge. And there Beth was, in the centre of the shot, beaming at the audience and looking like it was the best day of her life. She looked so happy, with her long hair, huge smile, cheeks flushed with the buzz of a great performance. She looked ready to take on the world. A smiling sixteen-year-old Mel was there too, at the other end of the row. She didn’t look different at all, gorgeous then and now. Both girls looked like innocents, untroubled and unguarded, with no idea of the loathing and jealousy and destruction that one of them would unleash on the other with her infidelity twenty years later, or how many lives would be ruined. How friendship would turn to hate.

My chest ached with the feeling of something lost.