Once he was back in his room, Harry shaved and dressed quickly, realizing that he hadn't eaten anything since he'd stepped off the plane. He locked his room, took the lift down to the ground floor and strolled across the lobby to the breakfast room. As he entered, the first person he spotted was Mr Bolton, sitting on his own, spreading marmalade on a piece of toast. Harry turned and fled. He thought about room service, but not for long.

His appointment with the ambassador wasn't until ten o'clock, and he knew from his notes that it would take only ten to fifteen minutes to reach the embassy on foot. He would have gone for a walk and looked for a cafe but for one of Sir Alan's repeated instructions: no unnecessary exposure. Nevertheless, he decided to leave a little early and walk slowly. He was relieved to find that Mr Bolton wasn't lurking in the corridor, the lift or the lobby, and he managed to make it out of the hotel without a further encounter.

Three blocks to the right, then two more to the left, and he would find himself in Plaza de Mayo, the tourist guidebook assured him. Ten minutes later, it was proved right. Union Jacks were being raised on flagpoles around the square, and Harry could only wonder why.

He crossed the road, not easy in a city that prided itself on having no traffic lights, and continued down Constitutional Avenue, stopping for a moment to admire a statue of someone called Estrada. His instructions told him that if he kept walking, in 200 yards he'd come to a set of wrought-iron gates emblazoned with the royal coat of arms.

Harry found himself standing outside the embassy at 9.33. Once around the block: 9.43. Once again, even slower: 9.56. Finally, he walked through the gates, across a pebbled courtyard and up a dozen steps, where a large double door was opened for him by a guard whose medals indicated that they had served in the same theatre of war. Lieutenant Harry Clifton of the Texas Rangers would have liked to stop and chat to him, but not today. As he was walking towards the reception desk a young woman stepped forward and asked, 'Are you Captain May?'

'Yes, I am.'

'My name is Becky Shaw. I'm the ambassador's private secretary, and he's asked me to take you straight through to his office.'

'Thank you,' said Harry. She led him down a red carpeted corridor, at the end of which she stopped, knocked gently on an imposing double door and entered without waiting for a response. Any fears Harry might have had of the ambassador not expecting him were proving unfounded.

He entered a large elegant room to find the ambassador sitting behind his desk in front of a vast semi-circle of windows. His Excellency, a small, square-jawed man who exuded energy, stood up and walked briskly over to Harry.

'How nice to meet you, Captain May,' he said, shaking him firmly by the hand. 'Would you care for a coffee, and perhaps some ginger biscuits?'

'Ginger biscuits,' repeated Harry. 'Yes please.'

The ambassador nodded, and his secretary quickly left the room, closing the door behind her.

'Now, I must be frank with you, old chap,' said the ambassador as he guided Harry towards a pair of comfortable chairs that looked out on to the embassy's manicured lawn that boasted several beds of roses. They could have been in the Home Counties. 'I have absolutely no idea what this meeting is about, except that if the cabinet secretary wants me to see you urgently, it has to be important. He's not a man given to wasting anyone's time.'

Harry removed an envelope from his jacket pocket and handed it to the ambassador, along with the thick file he had been entrusted with.

'I don't get many of these,' said His Excellency, looking at the crest on the back of the envelope.

The door opened and Becky returned with a tray of coffee and biscuits, which she placed on the table between them. The ambassador opened the foreign secretary's letter and read it slowly, but didn't say anything until Becky had left the room.

'I thought there was nothing new I could learn about Don Pedro Martinez, but it seems you're about to prove me wrong. Why don't you start at the beginning, Captain May?'

'My name is Harry Clifton,' he began, and two cups of coffee and six biscuits later, he had explained why he was staying at the Hotel Milonga and why he'd been unable to telephone his son and let him know that he should return to England immediately.

The ambassador's response took Harry by surprise. 'Do you know, Mr Clifton, if the foreign secretary had instructed me to assassinate Martinez, I would have carried out the order with considerable pleasure. I cannot begin to imagine how many lives that man has ruined.'

'And I fear my son may be next in line.'

'Not if I have anything to do with it. Now, as I see it, our first priority is to ensure your son's safety. Our second, and I suspect Sir Alan thinks it's equally important, is to discover how Martinez intends to smuggle such a large sum of money through customs. It's clear that Sir Alan believes'  -  he glanced at the letter  -  'that your son might be the one person who can find out how he plans to go about that. Is that a fair assessment?'

'Yes, sir, but he won't be able to achieve that unless I can speak to him without Martinez being aware of it.'

'Understood.' The ambassador leant back, closed his eyes and placed his fingertips together as if he was deep in prayer. 'The trick,' he said, his eyes remaining closed, 'will be to offer Martinez something money cannot buy.'

He jumped up, marched across to the window and stared out on to the lawn, where several members of his staff were busying themselves preparing for a garden party.

'You said that Martinez and your son aren't due to arrive in Buenos Aires until tomorrow?'

'Their SS South America docks at around six tomorrow morning, sir.'

'And you're no doubt aware of the imminent arrival of Princess Margaret, on an official visit?'

'So that's why there were so many Union Jacks in Plaza de Mayo.'

The ambassador smiled. 'HRH will only be with us for forty-eight hours. The highlight of her trip will be a garden party held in her honour here at the embassy on Monday afternoon, to which the great and the good of Buenos Aires have been invited. Martinez was not included, for obvious reasons, despite making it abundantly clear to me on more than one occasion how much he would like to be. But if my plan is to succeed, we're going to have to move, and move quickly.'

The ambassador swung round and pressed a button under his desk. Moments later Miss Shaw reappeared, pad and pencil in hand.

'I want you to send an invitation to Don Pedro Martinez for the royal garden party on Monday.' If his secretary was surprised, she didn't show it. 'And I also want to send him a letter at the same time.'

He closed his eyes, clearly composing the letter in his mind.

'Dear Don Pedro, I have great pleasure, no, particular pleasure, in enclosing an invitation to the embassy's garden party, at which we will be particularly, no, no, I've already used "particular", especially honoured by the presence of Her Royal Highness The Princess Margaret. New paragraph. As you will see, the invitation is for you and a guest. Far be it from me to advise you, but if there are any English men on your staff who might be able to attend, I think Her Royal Highness would consider that appropriate. I look forward to seeing you, yours etc. Did that sound pompous enough?'

'Yes,' said Miss Shaw with a nod. Harry kept his mouth shut.