Bloggs said: "Excuse me, but why are you so sure their man found out?"

Terry went to the door. "Come in, Rodriguez."

A tall, handsome man with jet-black hair and a long nose entered the room and nodded politely to Godliman and Bloggs. Terry said: "Senhor Rodriguez is our man at the Portuguese Embassy. Tell them what happened, Rodriguez."

The man stood by the door. "As you know, we have been watching Senhor Francisco of the embassy staff for some time. Today he went to meet a man in a taxi, and received an envelope. We relieved him of the envelope shortly after the man in the taxi drove off. We were able to get the licence number of the taxi."

"I'm having the cabbie traced," Terry said. "All right, Rodriguez, you'd better get back. And thank you."

The tall Portuguese left the room. Terry handed Godliman a large yellow envelope, addressed to Manuel Francisco. Godliman opened it- it had already been unsealed-and withdrew a second envelope marked with a meaningless series of letters: presumably a code.

Within the inner envelope were several sheets of paper covered with handwriting and a set of ten-by-eight photographs. Godliman examined the letter. "It looks like a very basic code," he said.

"You don't need to read it," Terry said impatiently. "Look at the photographs."

Godliman did so. There were about thirty of them, and he looked at each one before speaking. He handed them to Bloggs. "This is a catastrophe." Bloggs glanced through the pictures, then put them down.

Godliman said, "This is only his backup. He's still got the negatives, and he's going somewhere with them."

The three men sat still in the little office, like a tableau. The only illumination came from a spotlight on Godliman's desk. With the cream walls, the blacked-out window, the spare furniture and the worn Civil Service carpet, it was a prosaic backdrop for dramatics. Terry said, "I'm going to have to tell Churchill."

The phone rang, and the colonel picked it up. "Yes. Good. Bring him here right away, please, but before you do, ask him where he dropped the passenger. What? Thank you, get here fast." He hung up. "The taxi dropped our man at University College Hospital."

Bloggs said, "Perhaps he was injured in the fight with the Home Guard." Terry said, "Where is the hospital?"

"About five minuses' walk from Euston Station," Godliman said. "Trains from Euston go to Holyhead, Liverpool, Glasgow… all places from which you can catch a ferry to Ireland."

"Liverpool to Belfast," Bloggs said. "Then a car to the border across into Eire, and a U-boat on the Atlantic coast. Somewhere. He wouldn't risk Holyhead-to-Dublin because of the passport control, and there would be no point in going beyond Liverpool to Glasgow."

Godliman said, "Fred, you'd better go to the station and show the picture of Faber around, see if anyone noticed him getting on a train. I'll phone the station and warn them you're coming, and at the same time find out which trains have left since about ten thirty."

Bloggs picked up his hat and coat. "I'm on my way."

Godliman lifted the phone. "Yes, we're on our way."

There were still plenty of people at Euston Station. Although in normal times the station closed around midnight, wartime delays were such that the last train often had not left before the earliest milk train of the morning arrived. The station concourse was a mass of kitbags and sleeping bodies.

Bloggs showed the picture to three railway policemen. None of them recognised the face. He tried ten women porters: nothing. He went to every ticket barrier. One of the guards said, "We look at tickets, not faces." He tried half a dozen passengers without result. Finally he went into the ticket office and showed the picture to each of the clerks.

A very fat, bald clerk with ill-fitting false teeth recognised the face. "I play a game," he told Bloggs. "I try to spot something about a passenger that tells me why he's catching a train. Like, he might have a black tie for a funeral, or muddy boots means he's a farmer going home, or there might be a college scarf, or a white mark on a woman's finger where she's took off her wedding ring… know what I mean? Everybody got something. This is a dull job, not that I'm complaining-"

"What did you notice about this fellow?" Bloggs interrupted him.

"Nothing. That was it, see-I couldn't make him out at all. Almost like he was trying to be inconspicuous, know what I mean?"

"I know what you mean." Bloggs paused. "Now, I want you to think very carefully. Where was he going, can you remember?"

"Yes," said the fat clerk. "Inverness."

"That doesn't mean he's going there," said Godliman. "He's a professional-he knows we can ask questions at railway stations. I expect he automatically buys a ticket for the wrong destination." He looked at his watch. "He must have caught the 11:45. That train is now pulling into Stafford. I checked with the railway; they checked with the signalmen.

"They're going to stop the train this side of Crewe. I've got a plane standing by to fly you two to Stoke-on-Trent.

"Parkin, you'll board the train where it's stopped, outside Crewe. You'll be dressed as a ticket inspector, and you'll look at every ticket and every face on that train. When you've spotted Faber, just stay close to him.

"Bloggs, you'll be waiting at the ticket barrier at Crewe, just in case Faber decides to hop off there. But he won't. You'll get on the train, and be first off at Liverpool, and waiting at the ticket barrier for Parkin and Faber to come off it. Half the local constabulary will be there to back you up."

"That's all very well if he doesn't recognise me," Parkin said. "What if he remembers my face from Highgate?"

Godliman opened a desk drawer, took out a pistol, and gave it to Parkin. "If he recognises you, shoot him." Parkin pocketed the weapon without comment.

Godliman said: "You heard Colonel Terry, but I want to emphasise the importance of all this. If we don't catch this man, the invasion of Europe will have to be postponed possibly for a year. In that year the balance of war could turn against us. The time may never be this right again."

Bloggs said: "Do we get told how long it is to D-Day?"

Godliman decided they were at least as entitled as he; they were going into the field, after all. "All I know is that it's probably a matter of weeks."

Parkin was thinking, "It'll be June, then."

The phone rang and Godliman picked it up.

After a moment he looked up. "Your car's here."

Bloggs and Parkin stood up.

Godliman said, "Wait a minute."

They stood by the door, looking at the professor.

He was saying, "Yes, sir. Certainly. I will. Good-bye, sir."

Bloggs could not think of anyone Godliman called Sir. He said: "Who was that?"

Godliman said, "Churchill."

"what did he have to say?" Parkin asked, awestruck.

Godliman said, "He wishes you both good luck and Godspeed."

The carriage was pitch dark. Faber thought of the jokes people made, "Take your hand off my knee. No, not you, you." The British would make jokes out of anything. Their railways were now worse than ever, but nobody complained any more because it was in a good cause. Faber preferred the dark; it was anonymous.

There had been singing, earlier on. Three soldiers in the corridor had started it, and the whole carriage had joined in. They had been through "Be Like the Kettle and Sing", "There'll Always Be an England" (followed by "Glasgow Belongs to Me" and "Land of My Fathers" for ethnic balance), and, appropriately, "Don't Get Around Much Any More."

There had been an air raid warning, and the train slowed to thirty miles an hour. They were all supposed to lie on the floor, but of course there was no room. An anonymous female voice had said, "Oh, God, I'm frightened," and a male voice, equally anonymous except that it was cockney, had said: "You're in the safest place, girl they can't 'it a moving target." Then everyone laughed and nobody was scared any more. Someone opened a suitcase and passed around a packet of dried-egg sandwiches.