“You’ve been very clever,” Hoover snarled. “But you haven’t quite thought it through.” He glanced out of the window. We had reached the top of the circle, as high up as the Ferris wheel went. Suddenly Hoover fired. The glass door smashed. Tim leaped. The rain came rushing in. “An unfortunate accident!” Hoover shouted above the howl of the wind. “The door malfunctioned. Somehow it broke. You and your brother fell out.”

“No we didn’t!” Tim whimpered.

“Anyway, by the time they’ve finished wiping you off the South Bank, Fiona and I will have disappeared. The money is in a nice little bank in Brazil. We’ll move there. A beach house in Rio de Janeiro! We’ll live a life of luxury.”

“That money was meant for sick children!” I shouted. “Don’t you have any shame at all?”

“I cannot afford shame!” He gestured with the gun, pointing at the shattered glass and the swirling rain. “Now which one of you is going to step out first?”

“He is!” Tim pointed at me.

“No, I’m not,” I said. I turned back to Hoover. “It won’t work, Hoover. Why don’t you take a look in the next car?”

Hoover’s eyes narrowed. Fiona Lee went over to the window. There were about twenty people in the car above us on the London Eye. All of them were dressed in blue. “It’s full of policemen!” she exclaimed. She went over to the other side. “And the one below us! That’s full of police, too!”

“It must be their day off!” Tim said.

“Forget it, Tim.” It was my turn to smile. “You’ve been set up, Hoover. Every word you’ve said has been recorded. The car’s bugged. Your confession is on tape right now, and as soon as the ride is over, you and Fiona will have another ride. To jail!”

Fiona had begun to tremble. Hoover’s eyes twitched. His grip tightened on the gun. “Maybe I’ll kill you anyway,” he said. “Just for the fun of it . . .”

And that was when the helicopter appeared—a dark blue police helicopter, its blades beating at the rain outside the broken window. It had come swooping out of the clouds and now hovered just a few feet away. I could see Snape in the passenger seat. Boyle was in the back, dressed in a flak jacket, cradling an automatic rifle. I just hoped he was pointing it at Hoover, not at Tim.

“Why do you think the police released you?” I shouted above the noise of the helicopter. “I called Snape this morning and told him what I’d worked out and he asked me to meet you. You walked into a trap. He knew you’d feel safe up in the air, just the four of us. He wanted you to confess.”