There was one big lever that must surely be the brake. James pulled it, but nothing happened.

‘Hell,’ he said.

‘What is it?’ said Amy. ‘Why aren’t we moving?’

‘Obviously somebody needs to operate the car at the top,’ said James. ‘They need to fill it with water and release the brake. We’re stuck here, I’m afraid.’

But then, with no warning, the car moved forward with a jerk and they were travelling up the cliff.

Amy laughed with relief.

‘How did you do that?’ she said.

‘I don’t know,’ said James. ‘It’s a miracle.’

Halfway up the ‘miracle’ was explained as they passed the other car coming down.

It was packed with a group of confused and frightened guards from the dam, reluctantly trying to join the fight. The surprised look on their faces as they saw the two children serenely clanking up the hill past them was almost comical, and it was a few moments before they realised what was going on and started to shoot at them.

There was a sudden deafening racket as bullets slammed into the car. James and Amy threw themselves to the floor and they were soon lying in a thick carpet of shattered wood and broken glass. The cars quickly moved too far apart, though, for the men to fire accurately and neither of them was hurt. Once it was safe they got gingerly to their feet and brushed the debris from their clothing.

The rest of the jouney up passed without incident, but they forgot all about applying the brake when they reached the winch-house and the car slammed into the buffers, knocking them to the floor again. James was covered in tiny cuts but felt nothing. His body was flooded with adrenalin. No pain signals were getting through to his brain.

They dragged themselves back on to their feet and looked out. The place was deserted. James picked up the tommy gun. It was heavy and smelt of oil.

They jumped down and James went over to the cable that supported the car.

He aimed the machine gun and pulled the trigger, fully expecting that nothing would happen. But the gun came alive in his hands and jumped crazily, pushing him backwards. The din was terrific. He managed to hold it reasonably steady, though, and in a few moments the shredded cable gave way with a loud twang and the car rolled back down the cliff, picking up speed as it went.

‘There’s no way of anyone following us up here now,’ said James.

‘Yes,’ said Amy, ‘but how do we get down?’

‘We’ll worry about that later.’