She was about to give another roar when Scarface put his finger to his lips and went very still. In a blink she was out of Legoland and back into Zombieland. Forget theme-park rides: this was what it was like to be frightened. When you didn’t know what was going on. When you didn’t know where the enemy was. When you knew that there were things out there. Monsters. Real monsters, who wanted to kill you. Who would eat you if they could. Cannibals. Flesh-eating sickos.

Scarface made a movement with his hands that Ella understood – Go carefully, keep quiet, stay behind me – and walked out of the shop.

Not that she needed to be told to be careful.

Scarface crept on, hunched over, his spear held out in front of him. She stayed in his shadow, making herself small.

They made their way through the theme park, Scarface listening, listening, listening, although Ella could hear nothing. None of the paths here were straight; they wound through the trees and past the attractions, so that it was very hard to know what might be up ahead.

At last they rounded a corner and there ahead of them was Miniland, a sort of shrunk-down version of the world with all the famous places made out of Lego bricks, with buildings and roads and mountains and cars and people and rivers and boats … and sickos.

Three grown-ups were walking through it, looking lost. She heard Scarface sigh. Was this what they’d been tracking all this time? These three? Was it really worth coming all this way?

But, to be fair, she was glad there weren’t more of them.

They were going the other way and hadn’t seen Scarface and Ella. Scarface crept closer. Ready for the kill. Ella had seen dogs behave like this. All stiff and concentrating. There was going to be blood. Ella could see the colourful box of the Lego set sticking out of Scarface’s bag. It was always the same. Good things then bad things, good things then bad things.

Scarface got closer and closer, and still they hadn’t seen him.

The grown-ups were crossing London now; they’d passed the weird skyscraper called the Gherkin and were going past the Tower of London towards St Paul’s Cathedral. They looked like giants, or monsters from an alien invasion film, trampling the city. One of them, a big father wearing a long, dirty coat, brushed against Nelson’s Column as they crossed Trafalgar Square. When they got to Buckingham Palace, Scarface suddenly ran in and attacked, stabbing one in the back.

Ella looked away.

She didn’t want to see any more blood, any more killing, even though it had to be done. Every last grown-up had to die.