A drink now. Vodka with tonic to the brim of the glass. It’s gone inside three minutes so I pour another which is mostly ice by half past seven. How do I do this? How do I greet a friend whose life I placed in danger? MI5 used Saul to get to Katharine and Fortner. The four of us went to the movies together. Saul cooked dinner for them at his flat. At an oil-industry function in Piccadilly he unwittingly facilitated our initial introduction. And all without the slightest idea of what he was doing; just a decent, ordinary guy involved in something catastrophic, an eventually botched operation that cost people their careers, their lives. How do I arrange my face to greet him, given that he is aware of that?

At first it’s all nervous silences and small talk. There’s no big reunion speech, no hug or handshake. I fetch him from the taxi and we step into the narrow, cramped lift in my building and Saul says, ‘So this is where you live?’ and I reply, ‘Yeah,’ and then we don’t say anything for three floors. Once inside, there’s twenty minutes of ‘Nice place, man,’ and ‘Can I get you a cup of tea?’ and ‘It’s really good of you to put me up, Alec,’ and then he sits there awkwardly on the sofa like a potential buyer who has come round to view the flat. I want to rip out all the decorum and the anxiety and say how sorry I am, face to face, for the pain that I have caused him, but we must first endure the initiation rite of British politesse.

‘You’ve got a lot of DVDs.’

‘Yeah. Spanish TV sucks and I don’t have satellite.’

I am astonished by the weight he has put on, puffy fat slung round his neck and stomach. He looks worn out, barely the man I remember. At twenty-five, Saul Ricken was lean and lively, the friend everyone wanted to have. He had money in the bank, enough for him to write and to travel, and a medley of gorgeous, jealousy-inducing girlfriends. Everything seemed possible in his future. And then what happened? His adulterous French wife? His best friend? Did Alec Milius happen to him? The man facing me is a burnt-out case, an early mid-life crisis of exhaustion and excess fat. And it shames me that there is still a mean, competitive part of my nature that is glad about this; Saul is deeply troubled, and I am not the only one of us in decline.

‘Anybody else been to stay?’ he asks.

‘Not here,’ I tell him. ‘Mum came to a different place. A flat I was renting in Chamberí. About three years ago.’

‘Does she know about everything?’

This is the first moment of frankness between us, an acknowledgement of our black secret. Saul looks at the floor as he asks the question.

‘She knows nothing,’ I tell him.

‘Right.’

Maybe I should give him something else here, try to be a little more forthcoming.

‘It’s just that I didn’t have the guts, you know? I didn’t want to burst her bubble. She still thinks her son is a success story, a demographic miracle earning eighty grand a year. I’m not even sure she’d understand.’

Saul is nodding slowly. ‘No,’ he says. ‘It’s like having the drugs conversation with your parents. You think they’ll empathize when you tell them that you’ve taken E. You think they’ll be fascinated to learn that lines of charlie are regularly hoovered up in the bathrooms of every designer restaurant in London. You think that bringing up the subject of smoking hash at university is in some way going to bring you closer together. But the truth is they’ll never get it; in a fundamental way you always remain a child in your parents’ eyes. You tell your mum that you worked for MI5 and MI6 and that Kate and Will were murdered as a direct result of that, she’s not going to take it all that well.’

To hear him talk of Kate’s death like this is buckling. I had thought for some reason that Saul would let me off the hook. But that is not his style. He is direct and unambiguous and if you’re guilty of something he will call you on it. The awful shiver of guilt, the fever, washes through me as we sit facing one another across the room. Saul is looking at me with a terrible, isolating indifference; I cannot tell if he is upset or merely laying down the facts. There was certainly no suggestion of anger in the way that he broached the subject; perhaps he just wants to let me know that he has not forgotten.

‘You’re right,’ I manage to tell him. ‘Of course you’re right.’

He stands now, opens the window and steps out onto the narrow balcony which overlooks Princesa. Peering down at the street below, at the heavy traffic passing behind a line of mottled plane trees, he shouts out, ‘Noisy here,’ and frowns. What is he thinking? The characteristics of his face have been altered so much by age that I cannot even read his mood.

‘Why don’t you come inside, have a drink or something?’ I suggest. ‘Maybe you’d like a bath.’

‘Maybe.’

‘There’s not much hot water. Spaniards prefer showers. But then we could go out for dinner. I could show you round.’

‘Fine.’

Another silence. Does he want an argument? Does he want to have it out now?

‘Did you have any trouble with customs?’ I ask.

‘What do you mean?’

‘Leaving England. Did they search your bag?’

If John Lithiby had wanted to find out if Saul was bringing anything to me, he would have alerted Customs and Excise at Luton and instructed them to search his luggage.

‘Of course not. Why would they do that?’

He closes the balcony doors, muffling the sound of traffic, and begins pacing towards the kitchen. I follow him and try to seem relaxed, cloaking my paranoia in an easy, upbeat voice.

‘It’s just a possibility. If the cops want to check somebody’s stuff without raising suspicion, they hold everybody up and go through all the bags, maybe put a plain clothes officer in the queue to plant a rumour about a drugs bust or a bomb threat…’

‘What the fuck are you talking about? I went to HMV and Costa Coffee. Had an overpriced latte and nearly missed my flight.’

‘Right.’

More silence. Saul has found his way into my bedroom and is peering at the framed photographs on the wall. There’s one of Mum and Dad together in 1982, and a shot of Saul as a teenager with spiked hair. He stares at this for a long time, but doesn’t say anything about it. He probably thinks I hung it there this morning just to make him feel good.

‘I’ll tell you one thing about Luton airport,’ he says eventually. ‘Ann Summers. Don’t you love that? Just the thought process behind putting a lingerie shop in the pre-flight area. Couples going on holiday, probably haven’t had sex since 1996, then one of them spots the black suspender belt in the window. The shop was packed. Every father-of-three handing over wads of cash for a soft lace teddy and a pair of jelly handcuffs. It’s like announcing that you’re planning to have sex on the Costa del Sol. You might as well use the PA system.’

Taking advantage of his lighter mood, I fetch Saul a bottle of Mahou from the fridge and begin to think that everything is going to be OK. We make a plan to walk up to Bilbao metro to play chess at Café Comercial and he takes a shower after unpacking his bag. I notice that he has brought a laptop with him but assume that this is because of work. While waiting I wash up some mugs in the kitchen and then send a text to Sofía’s work mobile.

Have friend staying from England. Will call you after the weekend. Agree about the hotel…

A minute later she responds:

A friend? I did not think alec milius had friends… xxxx

I don’t bother replying. At 8.30 Saul emerges into the sitting room wearing a long coat and a pair of dark, slip-on Campers.

‘We’re off?’ he asks.

‘We’re off.’