The ball-bearing hit the ground just in front of the robots with a ferociously noisy explosion. Flames and smoke leapt greedily to be free, as if trapped inside the tiny space for so long, consuming the corridor and billowing out in a sudden gale. Ryan and Chantelle were thrown backwards, tumbling over the stone.

‘Whoa!’ Ears ringing, Ryan choked on the smoke. He turned to Chantelle. ‘The last boom was way smaller. You need to tell your mate to dial down her works in progress …’

Chantelle was sitting up, looking past him with a fixed expression.

Ryan frowned, shook her shoulder. ‘You all right?’

‘Are you all right, Ryan Sinclair?’ boomed a familiar voice.

Like a miracle, striding through the smoke, with arms stretched wide and a grin even wider, came the Doctor. She wrapped up Ryan in a humungous hug and yanked him to his feet.

‘Doctor, I was scared you’d really had it that time.’

‘Trust me, I’ve had it enough times in my life to send it straight back again.’ She stepped back from him, still beaming. ‘Now are you all right? And you?’ She hugged Chantelle too. ‘We’ve been worried sick!’

Chantelle got up, looking royally baffled. ‘We …?’

Ryan smiled as he took in the solid blue bulk of the TARDIS in the middle of the corridor between them and the remains of the robots; it must have materialised in the smoke and echoes of the blast. Yaz stepped out from behind the police box, carrying the fallen baseball bat.

‘Nice flying, Doctor,’ she said. ‘You homed right in on this thing.’ Then she ran up to Ryan too and grabbed him close. Ryan hugged her back.

Graham came out too, cradling the squirming metal Squidget in his arms. ‘Good to see you, mate! Sorry I can’t join in the hugs, got me hands full …’

Ryan laughed with happiness, but Chantelle was looking worried. ‘Don’t worry, Chantelle, that thing won’t bite …’

The smoke was dissipating, and the reunion greetings were kept short as the big man emerged cautiously from the corridor junction, wielding one of the Ratt’s weapons. His eyes flicked between Chantelle and the Doctor, Yaz and Graham. ‘Are these ones on our side?’ he said.

Chantelle gasped. ‘I can understand you!’

Graham nodded at the TARDIS. ‘Universal translator.’

‘Course it is.’ Chantelle smiled at the man. ‘Yes. These are our friends.’

‘The noise will bring more rat-things,’ the man said grimly. ‘We must prepare.’

‘He’s right,’ Ryan said. ‘We’re gonna have a fight on our hands.’

‘Where’s Ace?’ the Doctor said suddenly.

Yaz nodded, gesturing round at the ruined corridor. ‘Ace’s bat, Ace’s explosives, Ace herself …?’