Peri made the best of their enforced confinement on Astroville by spending further instructive and educational time in the archives.  She was curious to find pictures showing the Cartovallian royal family looking quite human, even though they had been taken some four thousand years before Earth developed interstellar travel.  The Doctor explained that the humanoid form was already widespread throughout the galaxy long before then, adding vaguely that 'my people' were partly responsible.  That was obviously another story in itself, but for the moment it was the mystery of Rovan that intrigued Peri.  One question still remained unanswered after five thousand years.  What could possibly induce a man who apparently had everything to give it all up?

Then, after a week, came a summons to police headquarters.

It was Jaharnus's sergeant who informed them that the report from Earth has been satisfactory.  They were no longer suspected of any involvement in the death of Hok and were free to leave Astroville.  The TARDIS key was returned to the Doctor, who signed a receipt for it without comment, though his quiet relief was evident.  Peri was less restrained.

'So the inspector didn't want to apologise face to face for keeping us here all this time, huh?' she said bitterly.

'I'm sure she was only doing her job,' the Doctor said, with what Peri considered infuriating forbearance.

'The inspector is involved in another aspect of the case,' the sergeant explained.  'She sends her apologies for any inconvenience - and hopes you have enjoyed your stay on Astroville.'

The Doctor hustled Peri out before she could say another a word.

'Even allowing for the circumstances, you seem very impatient to leave,' he observed, as they glided down the tower's thousand-metre-long passenger shaft.

Peri looked at him hopefully.  'Well, I was sort of wondering if we could use the TARDIS to go back in time and, maybe find out where Rovan leaves his treasure and -'

'Collect it for ourselves?'

'Sure, why not?  It wouldn't do any harm, if it's been lost all this time anyway.'

'Wouldn't it?  If Rovan's treasure was discovered before its proper time, how do we know what effect it would have on the last five thousand years?  The information in the archives that you've been studying might never have been written, which means a segment of your own timeline would have to change as well.  Perhaps Hok would never have obtained whatever information it was those three thugs were after, and so we wouldn't have disturbed them and the last few days would never have happened as they did, and we wouldn't be here now It would create a temporal paradox and I try to avoid them if possible.  Besides, spying on Rovan to see where he hid the treasure wouldn't be -'

'I know: it wouldn't be cricket.'  She was silent for a moment, then added thoughtfully: 'Still, there's no reason why we couldn't try to find it now, is there, since we've gotten mixed up in it anyway, I mean?  That's what everybody else seems to be trying to do.'  She frowned.  'I just wish I could remember those numbers Hok said.  They must have something to do with where the treasure is hidden.'

'You mean 385.06 by 946.573 by 157.67 positive?  Yes, I suspect they're galactic navigation coordinates.'

She looked at him in amazement, which rapidly turned to annoyance.  'Doctor!  Why didn't you tell me you remembered?  Do you know, how long I've been racking my brains over them?  And why didn't you tell Inspector Jaharnus?'