‘Is that relevant?’

‘It’s just background.’

‘I’ve been living here for about five years.’

‘And all that time working for Endiom?’

‘No. About half.’

‘What is the company’s link to Mikel Arenaza?’

‘There isn’t one, as far as I’m aware. Julian Church is a personal friend, that’s it. You’d have to ask him that.’

‘And you don’t know why Mr Arenaza was coming to Madrid?’

‘Like I said, I really don’t know.’

‘He calls you two hours before he’s due to get on a plane and doesn’t mention that he’s on his way here?’

‘It would seem so.’

Where is Zulaika getting such precise information? From Goena? Does he have a contact at the phone company? I need to find a way of deflecting his questions.

‘And you didn’t know where he was planning to stay?’

‘Look. You must understand that by asking me these questions again and again, you’re essentially accusing me of lying. And I don’t like being accused of lying, Mr Zulaika. I’ve told you that I met the guy for tapas two weeks ago. It’s just a grim coincidence that he should have telephoned me on the day he disappeared. I didn’t know he was coming to Madrid, so I didn’t know what hotel he was booked into. And I have absolutely no idea where the fuck he is.’

‘Of course.’

‘Fine.’

‘So you won’t mind if I go back to work.’

Over the next few days I experience an odd transformation in temperament, as if – like Zulaika, like the police – I cannot rest until I find out what happened to Mikel. Call it boredom, call it the smell of a conspiracy, but I can’t just sit at home, forever guarding my privacy, while his family and friends go nuts over the disappearance. If Mikel is shacked up with Rosalía, so be it. But something tells me that that is not the case. Something tells me that Arenaza is in deep, possibly unrecoverable trouble. And I am in a unique position to be able to help him.

Tracing Rosalía proves surprisingly easy. Mikel said that she was attending a conference on renewable energies at the Hotel Amara Plaza in San Sebastián when they met, so I simply call the hotel reception desk, pretend to be an employee of the Institute of Industrial Engineers putting together a newsletter for a website, and ask for a list of all the delegates who attended the conference to be faxed to me in Madrid. I give the number of a Mail Boxes Etc. outlet on Calle de Juan Alvarez Mendizábal and within forty-five minutes a six-page document has been spooled through to the shop. I didn’t even need to speak to the hotel’s PR department; the concierge did the whole thing for me without the slightest hesitation. On the third page of the fax, the name ‘Dieste, Rosalía Cristina’ appears next to her job description (‘Research Scientist’), a list of qualifications (including a five-year licenciatura from the Universidad Politécnica de Madrid) and the name of the company which employs her: Plettix S.L. A quick flick through the telephone directory locates their offices in Peñagrande, a godforsaken suburb in north-west Madrid. I call to arrange an appointment just after five o’clock on Thursday.

‘Good afternoon, could I speak to Rosalía Dieste, please?’

‘I’m afraid she’s left for the afternoon.’ The receptionist sounds chirpy and speaks with a heavy Extremaduran accent. ‘It was actually her last day here. Is there somebody else who might be able to help?’

I was going to pretend to be the science correspondent from an obscure British quarterly seeking an interview, but this changes the strategy considerably.

‘I’m not sure.’ Somehow I have to find a way of getting to Rosalía before she leaves the company for good. Thankfully the girl produces a little laugh, acknowledging that I have stumbled on a coincidence, and offers up a possible solution.

‘She had to go home early because we’re all meeting for a drink,’ she says. ‘Rosalía wanted to get ready.’

And I think quickly now.

‘Well, that’s actually why I was calling. I’m an old colleague of Rosalía’s from the Universidad Politécnica. I was supposed to be coming to the party but I wasn’t sure if it was today or tomorrow. She’s not answering her mobile. Do you happen to know where the bar is?’

And the receptionist, thank God, is the gullible, uninquisitive sort. ‘Sure. It’s just across the street. The Sierra y Mar, in the basement of the Edificio Santiago de Compostela. Do you know our offices?’

‘Of course. Of course.’ The thrill of the lie is like an old friend. ‘I can find it no problem.’

But there’s not much time. As soon as I have hung up, I grab a book, my coat and keys and head straight to the garage under Plaza de España. The Audi is low on petrol, but there’s enough fuel to get me twenty minutes north to Peñagrande, where I park beside the entrance to the metro station on a street devoid of people. The barrio is just like any other post-nuclear suburb in twenty-first-century Spain: a dusty wasteland of towering concrete apartment blocks, down-at-heel corner shops and tatty bars. Roads come at you from all directions. Across an abandoned lot strewn with litter and dead plants, the incongruously smart offices of Plettix S.L. rise up in a gleam of steel and glass. I walk down a wide, featureless avenue and cross a bridge spanning the M30 motorway. The Edificio Santiago de Compostela is one hundred metres downhill to the left, situated immediately alongside the Plettix headquarters and set back from the road by about thirty feet. The Sierra y Mar looks smart and clean and obviously serves as a meeting point for employees working in both buildings; a place to eat lunch, a place to drink coffee. I walk in and settle at the bar, just a few paces from the door, ordering a caña which comes with two gherkins and a pickled onion skewered onto a cocktail stick. There are four other customers on the premises: a construction worker sitting on a tall stool beside me; a courting couple unabashedly kissing at a table near the door; and an old man drinking coffee on the other side of the bar, which breaks at a 90-degree angle to my right. This is where the book comes in handy; with any luck, Rosalía’s colleagues will start pitching up for the party within about half an hour, and I will need something to occupy myself in the intervening period.

At a quarter to seven, two men wearing suits and chunky watches walk in and it’s obvious they’re the first guests to arrive. The owner has sectioned off about eight tables in the corner of the restaurant, decking them out with bowls of olives and crisps and several bottles of cava. This is my first problem: the tables are behind me and it will therefore be difficult to keep an eye on Rosalía from my position at the bar. The men shake the owner’s hand, order two beers and carry them over to the nearest of the tables. It’s possible to watch them in the reflection provided by a mirror hanging above the coffee machine, although the field of vision is small. Three minutes later, a half-dozen pack of Plettix employees comes surging through the door, laughter encircling them like smoke. Two of them are women, though neither strikes me as Arenaza’s type: he described Rosalía as ‘young’ and ‘Very beautiful’, but the two giggling mujeres bringing up the rear are puffy and pre-menopausal. She’ll doubtless be along in a minute.

Sure enough, at five past seven Rosalía Dieste walks in with a group of five colleagues. A small roar goes up, followed by clapping and even a whoop. The two men who had settled in the corner stand up and walk back towards the bar, and both of them kiss Rosalía on the cheek. She is standing right beside me now, about five feet five, seven or eight stone, a light tan and blonde hair – both out of a bottle – with clear skin, large breasts and wide, tired eyes. I was half-expecting Arenaza to walk in with her, but one of the women says, Where’s Gael?’ and I assume that’s the name of her regular boyfriend. Her voice is quiet and intelligent and she seems genuinely affectionate towards colleagues who have clearly grown fond of her. Is she leaving to start a new life with Mikel? Has she any idea what mysteries she has left in her wake? On instinct, I would say that she looks troubled, but it is always best – particularly where attractive women are concerned – to take nothing on gut reaction. Glass in hand, she accompanies the group to the back of the room and calls out ‘Joder!’ when she sees the bottles of cava on the table. After that, it’s hard to hear what anybody is saying. The tables are at least fifteen feet away and obscured by a large pillar with a fire extinguisher bolted to it. Rosalía is rarely visible in the mirror and all conversation is lost in the general din of the party. To make matters worse, a diarrhoea of Spanish pop music is continually pouring out of the speakers, song after song about ‘amor’ and ‘mi corazón’, the soundtrack of Benidorm and Marbella. Now and again I will turn round and check my watch, as if frustrated and waiting to meet someone, but my surveillance becomes increasingly pointless. If I am going to follow Rosalía this weekend she cannot become aware of me, nor suspicious of the fact that I am sitting alone at the bar. So, having settled the bill, I walk back to the Audi and drive it to a parking space immediately in front of the building. Through the rear-view mirror I have clear sight of the entrance to the restaurant and, with any luck, will be able to follow Rosalía as soon as she leaves to go home.