But he knew better than to make trouble: some southeastern European countries had been known to refuse CIA personnel entry, or to mire them in a maze of bureaucracy and paperwork before they did so, sometimes delaying them by days – and a delay was the one thing Sami could not afford. And it was understandable, under the circumstances, that the normally beefy security presence was now on steroids. He wasn’t going to get anywhere with anything less than complete cooperation.

So he zipped his mouth and stood there patiently as the soldier picked through the contents of his bag, and then inspected his passport and visa again. Eventually, Sami was given the all-clear, his passport and visa were stamped and his backpack roughly repacked. He thanked the soldiers politely and made his way out of the terminal and into the grey and crisply cold afternoon.

Mav was waiting for Sami out the front, parked directly – and illegally – in front of the main exit. When Sami reached him, Mav got out of the car, shook his hand and popped the trunk of the black BMW hire car. Sami threw his backpack in, then Mav pulled a heavy black overcoat out and pressed it into Sami’s hands. ‘You’ll be needing this, sir. It gets cold enough to snap your balls off here.’ Sami shrugged the overcoat on and got into the passenger seat as Mav started the engine.

Sofia would have been a ghost town had it not been for the heavy military and police presence. The only people Sami could see, as Mav went about breaking every road rule in Bulgaria, were in uniform. The capital, set at the foot of the snow-capped peaks of the Vitosha mountain range, was undeniably beautiful. But today it was also austere – its usually bustling population of 1.3 million residents opting to staying indoors after 412 people had been killed the day before in the worst terror attack in the country’s history.

It was also Europe’s most lethal terror attack, eclipsing the death toll from the Beslan School Hostage crisis in Russia in 2004, when 334 people were murdered. But it wasn’t the dead Sami was interested in, it was the living. Finally, they had a witness. Witnesses, in fact. Four.

‘It’s all there,’ Mav said as he broke yet another road rule – both hands off the steering wheel – and passed Sami a file. ‘I interviewed the three that could talk; the other guy is in a coma.’

Sami pulled out the first transcript and read as Maverick sped towards the CIA office in central Sofia.

Statement of Mr Yavor Dimitrov (26 September, 9 am, interviewed by Special Agent Ryan Smith and translated by Ivan Stoyanov, Second Main Directorate, Bulgarian Committee for State Security)