‘I’m afraid that’s not quite accurate. These grooves are narrow and deep and only appear on the back. Now look at this. That’s the cord, laid beside the marks. You can see it tallies. So far you are right, Carmichael. But you see that the higher marks cross each other in the form of an X with a line underneath. Have another shot. What are they?’

From somewhere towards the back a doubtful voice uttered the word ‘flagellation’ and followed it with an apologetic little cough. Someone else made the noise ‘gatcha’ upon which there was a muffled guffaw.

‘You’ll have to do better than that,’ Alleyn said. ‘However: to press on with Mr Fox’s investigations. He found nothing else of interest at the Crossdyke end and moved to the stretch of river below Ramsdyke weir where the body was found. Above Ramsdyke near the hollow called Wapentake Pot, the road from Crossdyke and Tollardwark was undergoing repairs. There were loose stones and rubble. It crosses Dyke Way and Dyke Way leads down to a bridge over The River where the Roman canal joins it. Downstream from here is the weir with its own bridge, a narrow affair with a single handrail. It’s here that the effluent from a factory enters the mainstream and brews a great mass of detergent foam over the lower reaches.

‘The weir bridge is narrow, green, wet and slithery with foam blown back from the fall. It is approached from the road by concrete steps and a cinder path.

‘Along this path, Mr Fox again found a thread or two of dark blue synthetic caught on a bramble. Here’s the photograph. And I may tell you that a close search of the pyjamas revealed a triangular gap that matched the fragment from Crossdyke. Classic stuff.

‘The path is bordered on one side by a very old wall from which a number of bricks had worked loose.

‘Now for the weir bridge. Nearly three days had passed between the night she disappeared and our work on it. A pretty dense film of detergent had been blown back and it was a particularly awkward job to examine it without destroying any evidence there might be. However. There was a notice warning people that it was dangerous to use the bridge and the lock-keeper said he didn’t think anyone had been on it for at least a week.