They had visitors the next day.

Christian was standing on deck and smoking his cigar.

Suddenly he was no longer alone. A voice said:

"At last, Captain!"

He turned and saw many big bald heads. The Brains! One of them was Waldo. He raised his decapitator. There was a flash - and nothing happened. Paul's energy barrier protected Christian.

Waldo was shaken.

There is a Watcher here," he said - and then Paul came up on deck.

Waldo spat. All the Brains were standing and looking at Paul

"You must return to the future," said Paul quietly. "If you don't. I shall have to use force."

Waldo laughed.

"It is well known," he said, "that the Watchers do not kill. You can do nothing. We are not afraid of you!"

Christian was angry. He threw away his cigar and raised his automatic.

"I am not a Watcher," he said," and I kill."

Paul turned his head.

"It is useless to shoot, Captain," he said. "My energy barrier works both ways - it will protect them, too"

"I'll kill you one day!" shouted Waldo to Christian. "You shan't always escape me."

Paul looked at Waldo.

"Your time machine is in the hands of the Watchers," he said. "You are free only while you remain here - and I shall make this age unbearable for you."

Waldo was looking at him with angry eyes.

"You Watchers have done what you liked too long," he said. "You have upset our plan - but that won't save you. We'll see what happens -"

Paul interrupted: "I shall not allow you to interfere with the natural course of history. Return to your own time, and I'll do what I can to help you."

"Help!" Waldo spat. "We want no help from the Watchers. You will see what will happen - we shall destroy Earth completely!"

Paul looked troubled, and Christian said: "Switch off your barrier and shoot them!"

"He won't do that!" Waldo laughed. "A Watcher will never kill!" He touched the crystal on his belt and disappeared with the rest of the Brains.

Christian turned to Paul.

"You heard what he said - the'll destroy Earth. There won't be any future if we don't kill them. There is no other way."

Paul sighed unhappily.

"There must be another way," he said.

He went down into the cabin. He took some wires out of his metal box and began making some complicated device

"It will be good if you inform your government of this new threat of the Brains," he said to Christian. "It will take me some time to build the weapon which I am making, and who knows what the Brains may do during this time."

"This weapon which you are making - will it stop the Brains?"

"Yes, it will stop them."

Christian ran up on deck, jumped on the shore and hurried to the nearest telephone.

The Imperial Technical Institute occupied a very large territory; hundreds of specialists worked in its laboratories and workshops; and its stores contained materials for production of anything from shampoo to an atomic bomb.

The Brains came there at night. The guards were decapitated at once, and behind the Institute's massive walls the Brains began making weapons of destruction.

They worked hard. In the stores of the Institute they found all the necessary materials. The Brains were very many, and they all were clever specialists, so their work went on very fast.

Christian was back in London. He was speaking to the Prime Minister and the head of Military Intelligence. He had just finished telling them about Paul's meeting with the Brains, when the telephone rang. The Prime Minister took up the receiver and listened. Then he put down the receiver.

"Operation Finish," he said, "is starting now."

The Old Man jumped up.

"Have they found the Brains?" he asked

"Yes," said the Prime Minister, walking to the door. "We must go to the Headquarters of the Operation. Captain Christian, you may go with us."

They hurried along the corridor and up a staircase. They entered a room and went up to a large table in the middle. There were several officers of high rank near the table. On the table there was a large map, and two girls moved coloured pieces of plastic on it, as the radio-telephone announced coordinates.