Graham was still fussing over Ryan. The lad had had a lucky escape by the sound of it; another second and there might have been two bodies to deal with. Ryan was making light of it, of course, embarrassed by the attention that his granddad was paying to him. A lot of that bravado seemed to be for Chantelle’s benefit; he was obviously smitten.

For her part, Chantelle didn’t seem to be too bothered by Ryan’s clumsy attempts at flirting. Far from it. In fact she seem to have taken a bit of a shine to him too. Ace smiled to herself. Given her track record – and although he was way too young for her – she could probably do a lot worse.

Yaz was with the Doctor, watching the autopsy intently. Ace wanted to like the girl, she really did, but Yaz wasn’t making it easy. She seemed suspicious of everything. The two of them needed to sit down and have a proper talk at some point.

Ace sighed. There was too much else to concentrate on to worry about that right now. She turned her attention back to the readout on the benchtop spectrometer. She’d run several tests on the unpleasant slime on the assumption that it was venom of some kind, but the results were indicating something different.

She opened the centrifuge and lifted out one of the test tubes, holding it up to her nose. Despite the fact that over an hour had gone by, the mucus was still as pungent as before.

‘Professor?’

‘Hmm?’ The Doctor didn’t look up from her work.

‘I don’t think this is a venom at all.’

‘Oh?’

‘I think it’s some kind of hormonal scent marker.’

That got the Doctor’s attention. ‘Really?’ Putting down her scalpel she joined Ace at the spectroscope, slipping on a pair of wire-rimmed spectacles and peering intently at the readout. ‘You’re right. Pheromones, volatile hydrocarbons … It does seem to be some kind of tracking marker.’

‘So the abducted girls were tagged for collection?’ Yaz had joined them too. ‘Could that ship be a collection device of some kind?’

Ace was impressed; Yaz really didn’t miss anything. ‘All right.’ Ace nodded at the alien body on the bench. ‘So we know that it is using its saliva as some kind of marker. Any idea what it is yet?’

The Doctor nodded. ‘It’s a Ratt. It looks so messed up because we caught it mid transformation.’

‘Transformation?’ Ace frowned. ‘It’s a shapeshifter?’

‘More of a therianthrope. Like Ogrons or Quarks, they’re used by various nasty races as hench-aliens for hire. They don’t have advanced shapeshifting ability, but it can certainly hop between humanoid and animal form. It was obviously trying to transform back into its animal state when the train hit it. Messy.’

‘So all those rat sightings …’