‘There was just one other thing,’ Bonilla says, so calm and relaxed it seems impossible to believe that he might be setting me up.

‘And what’s that?’

‘We are assuming that you know about Rosalía’s family? About her step-father?’

‘No.’

He is looking at my cigar, following the smoke as it drifts in thick puffs towards the roof of the marquee.

‘It cannot probably be important because it was very long ago, but it was the only thing of significance in the investigation. I found out this morning.’

‘Yes?’

‘When Rosalía was six, her father died from liver failure. He was apparently a borracho, a drunk.’ This seems to amuse Bonilla, who finishes the last of the red wine before leaning back in his chair. ‘Her mother, the woman she visited in Tres Cantos at the weekend, went on to marry a member of the Guardia Civil in Madrid. His name was Pasqual Vicente. He became – how would you say it? – a substitute father to Rosalía, and to her brother, Adolfo. But he was particularly close to the girl.’

‘How do you know this?’

‘I find the interviews. The police reports.’

‘Police reports? I’m not following.’

‘Vicente was blown up by an ETA car bomb in 1983. Close to the Chamartín station. Killed alongside a colleague in the Guardia Civil. You look surprised, Mr Thompson. You start to look pale. Is everything all right?’

24. El Cochinillo

It was a honey trap. I allowed the simplicity of Rosalía’s deceit to obscure the truth about Arenaza’s disappearance. She posed as his lover, lured him to Madrid and – most probably – Sellini did the rest. Walking in the Casa de Campo after Bonilla has paid the bill, taken my cheque and left, I put the pieces together with ease. Mikel’s death was revenge for the step-father’s murder, pure and simple. It’s time the police knew about that. It’s time to call Patxo Zulaika.

Back at the flat I find his phone number and dial it just after five o’clock in the afternoon. A full confession to Goena is not an option: instead, I will tell Zulaika that Mikel briefly mentioned he had a mistress called Natalia or Rosalía in Madrid who worked as a lawyer or industrial engineer. It was something he said over dinner that completely slipped my mind. A guy as professional as Patxo should be able to put the pieces together based on these simple clues. Unless Bonilla already knows the whole story. Unless he has already gone to the cops.

But Zulaika isn’t answering his phone. According to a message in crackled Basque and Spanish, he will be out of the office until Monday. He doesn’t leave a contact number, but suggests calling one of his colleagues at Ahotsa ‘in the event of an emergency’.

‘Hello, Mr Zulaika. This is Alec Milius. You may recall that we spoke about Mikel Arenaza’s disappearance when you were in Madrid a couple of weeks ago. It may not be important, but I’ve remembered something that could be interesting for you. Would you give me a call when you get this message? Gracias.’

Sure enough, the internet is choked with stories about the Chamartín bomb. Pasqual Vicente was a 34-year-old Guardia Civil, respected and well liked by his colleagues, intelligent and ambitious and clearly going places with his career. He was called to the railway station on the morning of 6 June 1983 to investigate a petty theft. He arrived in a squad car with his partner, Pablo Aguirre, and spent about an hour interviewing a woman who claimed that her bag had been stolen from a café on the station concourse. It later transpired that the woman – who disappeared – had given a false name and that no such theft had occurred. Instead, the absence of the two police officers from their car gave three ETA operatives time to attach an explosive device to the chassis. When Vicente turned the key in the ignition, the entire vehicle was blown apart, killing both of them instantly and injuring a number of passers-by. Rosalía Dieste was eleven. Her brother was eight. Their mother, already widowed once, had to bury a second husband before she was forty years old.

For a change of scene, and to clear my thoughts, I take a drive out to Segovia and eat cochinillo for lunch at Mesón de Cándido, the city’s best-known restaurant, situated below the aqueduct at Plaza de Azoguejo. It’s about an hour’s drive north-west of Madrid, quicker than it used to be now that they’ve extended the motorway, and it feels good to be free of the city, just strolling around the cathedral, the Plaza Mayor and the Alcázar. Zulaika must be away on holiday because he hasn’t rung back. Once he returns my call on Monday I can begin to put the whole Arenaza episode behind me and maybe think about going home to London. I can’t afford to become associated with a murder enquiry, particularly one with links to an organization like ETA. It was stupid of me to get sucked back into this world. As if unable to escape from a drug whose effects first ensnared me as long ago as 1995, I could not see a way of ignoring what had happened to Mikel. The possibilities seemed too great, the chances for excitement too much for me to resist. And now, for the second time in my life, I have blood on my hands. First Kate, now Arenaza. The secret world betrays me. To hold out any hope of salvation I have to cut myself off from it entirely.

But then Alfonso, the concierge at the Hotel Carta, rings the Telefónica mobile with a piece of information that immediately tests my resolve.

‘Señor Thompson?’

‘Sí, Alfonso. Qué tal?’

‘Abel Sellini is checking out.’

‘Checking out?’

‘Five minutes ago he stopped to talk to me in the lobby and asked for a taxi to take him to Barajas airport at five fifteen.’

That’s in just under two hours.

‘OΚ. Thanks for letting me know.’

In truth, I don’t even consider the consequences of not continuing my surveillance. You might as well ask me to cut off an arm. I am designed for this.

‘Did he say where he was going?’

‘No, sir. I just thought you might want to know.’

At the very least I can tail Sellini to the airport, find out what flight he’s on, try to work out a final destination. That is the sort of information that would be useful to the police. This is the individual, after all, who most probably murdered Mikel Arenaza. I have a responsibility to follow him. A duty.

So I sprint in bright sunshine from the cathedral all the way down the eastern edge of Segovia to the space where I parked the car off Plaza de Azoguejo. It’s about a half-mile run and by the time I have unlocked the doors and thrown my coat in the back of the Audi my body is drenched in sweat. There are lines of traffic at every set of lights leading out of the city but I horn and barge and cut my way to the front of the queues and make it out onto the carretera by ten to four. By five, having driven at a steady 170 kph all the way home, I’m passing through Moncloa. With luck I should be outside the Carta within a quarter of an hour.

‘Has he left yet?’ I ask Alfonso in Spanish, dialling his mobile from a set of lights on Gran Vía.

‘Sí, Señor Chris,’ he says, sounding rushed and anxious. ‘He came downstairs five minutes ago to pay his bill. He asked me to have the taxi waiting and I don’t know what to do. There’s a rank directly outside. There are always cars there. I will have to go down and flag one.’

‘Well, at least get me the number plate. At least try and stall him. Have a chat before he leaves and ask where he’s going. I’ll be there in less than ten minutes.’

As it turns out, I’m there in five and park the Audi in a slot immediately behind the taxi rank, about fifty metres short of the slope leading up to the hotel. Alfonso isn’t answering his phone and there’s no sign of Sellini. I walk slowly up towards the lobby doors, prepared at any moment for either one of them to emerge. A second porter, whom I don’t recognize, is operating the main door and I walk past him into the lobby. Sellini and Alfonso are engaged in conversation near reception. Alfonso looks up, registers my presence with a shift in the eyes, and then proceeds to drag a trolley laden with luggage out through the main entrance. Turning away from them, I walk back outside and down the slope towards the Audi. There are two cabs on the rank and the chances are that Sellini will get the first of them. Then it will just be a simple question of following him out to Barajas.