'Have you got those rocks on a static 3-D viewer?'

'We have, but I wouldn't bother.'

Eastlake had obviously been briefed. Last night Tilson had just told me to keep the rendezvous and that was all, so I hadn't reported at the Bureau this morning on my way here; but they'd briefed these chaps to run this film without telling me what I had to look for and there must be a good reason.

The desert spun and tilted, the group of rocks changing shape as the angle of view turned through its conic vector, the light-and-shadow corrugations of the dunes shifting definition like water flowing in slow motion. It was all I could see.

'Can we have a few stops?'

The squadron-leader spoke to the girl and she began breaking it up into ten-second runs and I still couldn't get it. The whole scene's slow revolutions were becoming mesmeric and I shut my eyes to prevent strain, viewing for a few seconds and trying to coincide with the rhythm of the stops, resting at intervals and waiting till the after-image had faded under my closed lids. I knew now why they'd been warned not to tell me what I was expected to look for: the inter-reactive process of eye and brain can play tricks and sometimes you can see things only because you've been told they're there.

'Would youlike some run-backs?'

'We can try.'

He told the girl and the scene began swinging anti-clockwise at precise intervals with five-second stops. It didn't make any difference: I was looking at the same thing in a mirror. There's no point in run-backs unless you think you've spotted something and want to recap and I hadn't spotted a bloody thing and I was getting fed-up. The heat of the projector was adding to the heat of our bodies in here and there was nothing much left to breathe and I thought it'd be nice if a girl came round with a tray of Dairymaid.

The dunes flowed under my eyes.