Will looked at Yaz, who shrugged blankly. ‘We don’t have time to play guessing games, Doctor.’

The Doctor took the hint. ‘Time-storming Ace to Svartos in 1987 was a one-off trip – Fenric, or whoever his agent was, didn’t need to cover his tracks. But now, in 2020, they’re time-storming a lot of people and they don’t want anyone to know …’

‘So they turn down the power?’ Yaz concluded.

‘Right.’

‘But that doesn’t make sense. Ace’s magic bat would still be showing, and you said there’s no trace of them anywhere within range.’

Will looked ashen. ‘They’ve been obliterated.’

‘Well, that would make no sense at all, would it?’ The Doctor snorted. ‘Why go to the trouble of finding them and snatching them off-world just to obliterate them?’

‘Then, if they’re not anywhere within range … they must be out of range.’ With a thrill of dread, Yaz suddenly understood where the Doctor was leading them. ‘Boosted out of range? To another collector station, that boosts them on again?’

The Doctor grinned, nodded excitedly. ‘Perhaps a whole chain of thousands of collectors working in relay! Or just a few, flitting in and out through wormholes, each passing the others, further and further out on a random course. Boosting the low-level signal on and on through time and space …’

‘The same way satellites boost phone signals around the planet,’ said Will, ‘only on an intergalactic scale?’

‘Or the same way spoof servers can re-route internet traffic, completely obscuring the actual destination. Because ultimately, it’s the destination we need to know.’

Abruptly, the Doctor stormed outside. Yaz and Will swapped a glance and followed her.

‘Can’t you just scan for the bat?’ said Yaz. ‘I know it’s like looking for a needle in a haystack …’

‘More like looking for a sub-atomic needle in a hundred thousand million, billion haystacks,’ the Doctor told her. ‘The universe is a very big place.’ She had crossed to where Squidget was lying in the regeneration cradle, and studied the readout. ‘Question is, how much do the Astingir know about where to look? They’re dedicated to destroying all Wraith technology. I doubt their War Chariot randomly picked on that collector orbiting the Moon – it’s simply the first in the chain.’

‘Unless they followed it backwards,’ said Will grimly.

Yaz started in alarm. ‘If they did, that could mean there are no collectors left to boost Ace and the others onward!’

‘Meaning they could all be lost,’ Will realised. ‘Scattered in time and space …’

‘Never say die! We need to know the locations of the other stations in the chain.’ The Doctor powered down the cradle. ‘With the proper spatio-temporal coordinates, we can focus the search, speed up our rescue operation.’

Will raised his eyebrows. ‘And just how do we find the exact spatio-temporal coordinates?’