Customs Officer Harry Standish did not hear the flight departure announcement, but he knew that it had been made. He had a special interest in Flight Two, because Judy would be travelling on it. Judy was a fine young girl, and a great favourite with her uncle Harry.

He was a very busy man, but he found time to walk over to Gate 47 to say goodbye to her. When she had gone he stood near the gate for a while, watching the last few passengers hurry by Tanya Livingston was watching them, too.

A tall, fair young man went through the gate. He seemed to be the last one. Tanya left as soon as he had disappeared, but Standish saw two other people arrive. One of them was a small figure in black, a little old lady.

'My son just went through this gate,' he heard her say to a ticket agent. 'He's a tall, fair young man. He's forgotten all his money. May I take it to him, please?'

The agent was busy with his papers. 'Go and ask an air hostess,' he said, smiling kindly at the old lady.

The last passenger came a moment later. He was a thin man who was carrying a small case. Something about this man attracted the officer's attention. He knew immediately, from his long experience in dealing with the public, that there was something strange about him.

***

He had successfully bought and posted the insurance policy, and he was on the plane. D. O. Guerrero felt full of confidence. All his difficulties were over.

'Have a pleasant flight, sir,' the agent at the gate had said to him.

His seat was by the window. There was an empty seat in the centre, and then another man. He closed his eyes. He felt happier than he had for a long time. He put his fingers inside the case and felt the important piece of string. When he pulled it, the plane would be destroyed immediately.

Immediately? He hoped that there would be a last second in which he would know about his success. And then - thank heavens - no more.

He opened his eyes. One of the air hostesses was counting the passengers.

During the count, Mrs Ada Quonsett was hiding in one of the toilets. If she could remain hidden now, she knew that she had a good chance of reaching Rome. It had been a nasty shock seeing that red-haired woman at the gate, but in the end all her plans had gone well.

She opened the door a little, and looked out. There was an empty seat between two men, and she decided to slip into it. As she did so, she was included in the passenger count.