‘What’s going on?’ said a voice.

‘We come to rescue you,’ said Achilleus. ‘Open up.’

‘We’re not unlocking these gates,’ said another voice.

‘Do as he says,’ said Jackson wearily. ‘They’re friends.’

She heard a rattle of keys, a clank, and the gates swung open. The big girl, Whitney, took most of the kids inside and Jackson was left with Achilleus, Paddy and seven of her team.

‘We climbing,’ said Achilleus, and he looked up towards the roof.

Maxie was helping Ollie’s team drag the last of the dead grown-ups out through the front doors. There was a dark smear across the tiles. She took the body to the wide, shallow steps at the front and hauled it down, its head bumping as they went. She was too pumped up to feel frightened. She had a job to do and that was all. She knew she’d pay for it in the morning. She’d be exhausted and moody and short-tempered, but if they could clear the museum tonight then she could sleep all week if she wanted. Hell, she had no right to be tired. She’d spent most of the last day lying in bed. She supposed it was the stress that took it out of you, though.

She dumped the body with the others at the bottom of the steps and went back inside where she helped one of the museum kids secure the doors.

‘So we’ve got the blue zone, yeah?’ she said to him. ‘Talk me through it.’

‘It’s about ten rooms. Half of them are locked, though, so we shouldn’t need to check them.’

‘OK. And the others?’

‘Two main corridors. And the mammals gallery, human body and dinosaurs.’

Oh great. Just great …

Blue’s party had already met two grown-ups halfway down the stairs to the lower level, wandering, confused. They didn’t look too dangerous, more scared than anything, pale and thin and weak. They’d somehow got through the doors and now didn’t really know what to do. Blue wasn’t in the mood to show them any mercy, though. He wanted this night over. He wanted to sleep in peace.

‘I’ll do it,’ he said, holding Boggle back, and clubbed the grown-ups to the floor. Then smashed their skulls against the steps.

‘We’ll collect the bodies later. Try and remember where they’re lying.’

At the bottom of the stairs they found three more grown-ups, but these ones were already dead. There was the body of a young girl lying with them; they’d obviously dragged her down here before they killed her.

Blue shone his torch both ways down a long straight corridor. Pipework, wiring and strip lighting ran along the ceiling; ancient filing cabinets, piles of boxes and junk lined the walls.

‘How far to the doors we need to lock?’ Blue asked.

‘There’s a sort of crossroads to the right,’ said Boggle. ‘A door there.’