‘Apart from the straw and the saddlebags,’ Ryan said, and they both smiled. Then Ryan grew serious. ‘Listen, Granddad. Ace told me that—’

He quickly shut up and shoved the torch back in his pocket as an invisible door in the wall cranked open. Two of the centaur-things pushed into the cell, dominating the space. Graham felt uneasy just looking at them; they looked so familiar in some ways, but so wrong. It was the little heads that did it, he decided: heads resembling a horse’s but the size of a human’s. Both the creatures were ashen white in colour, with manes as black as their eyes, plaited with strips of metal. One wore golden armour, the other silver.

The golden one flared her nostrils. Graham saw the white hairs around her eyes; she’d been around a bit, this one. ‘I am Legate Aquillon, Charioteer-General in the service of Operation Deep Avenge.’ She tossed her head towards her fellow. ‘This is Centaurion Masst.’

Graham cleared his throat, stepped forward. ‘I’m Former Bus-Driver Graham O’Brien, and this is, um, Teen Loiterer Ryan Sinclair.’

Ryan flashed him a look, mouthed, ‘Seriously?’

‘We’ve done nothing wrong, ma’am,’ Graham insisted. ‘This boy was kidnapped from Earth. I was on that space station cos we were trying to rescue him. Me and the Doctor.’

‘The Doctor is an enemy of our race,’ said Aquillon. ‘A known war criminal with the power to change appearance: an ally of the Wraiths and murderer of our kind.’

‘No way,’ said Graham. ‘Wrong person.’

‘DNA scan proved her culpability.’ Aquillon swept her fierce gaze onto Graham. ‘If you are in her service, you will be executed.’

Ryan swallowed hard. ‘We’re not in anyone’s service. We’re not military, nothing like that, and neither’s the Doctor.’

‘You are her associate, then.’ Aquillon pushed her head closer to Ryan, eyes shining. ‘Her spy.’

Ryan met the dark depths of her gaze. ‘Her friend.’

‘The Doctor’s not an ally of these Wraith things!’ Graham protested.

‘Permission to use the think-scan on them, Legate?’ Masst tried to come between Aquillon and Ryan. ‘If our prisoners are telling the truth …’

Aquillon snorted. ‘Are the think-scans even still functional after all this time?’

‘One is.’ Masst sounded defensive. ‘I’ve cannibalised parts from the others to sustain it. They’ll give us the answers we want—’

‘Nothing lasts, does it, Centaurion?’ Aquillon’s voice was low and husky. ‘Better we learn to get answers for ourselves.’ She pulled down hard on the chain around Ryan’s neck, and Ryan fell to his knees with a gasp. ‘I repeat: you are an associate of a known war criminal, Ryan Sinclair!’ The rasping voice was more insistent this time. ‘You are her spy.’

‘No!’ Graham started forward, but Masst raised an ash-white hand. ‘The Doctor was trying to save a whole bunch of kids who were kidnapped from planet Earth by these alien rat-things.’