There was the sound of a loud groan of machinery, and I could see the wall of the lock lifting at the far end. This put anyone in the lock in mortal danger from the severe and sudden undertow that opening the sluice gates would cause. Holmes and Buttons would be sucked into the slacker tunnel just as Dillie had been!

Both heads surfaced. Buttons panicked, clutching at Holmes, his hands raking my friend’s face, ripping at his hair.

‘Holmes, the lock!’ I shouted.

But Buttons continued thrashing about, his arms flailing, striking Holmes and dragging his would-be rescuer underwater again in a desperate dance of survival.

Holmes surfaced. ‘Wats—!’ he shouted, but was cut off when Buttons pulled them both under again. Both heads surfaced, gasping, then there was a loud whooshing sound as the lock gates fully opened, and both of them were abruptly sucked under as the rushing waters pulled them towards the dangerous tunnels.

‘Holmes!’ I cried. I raced off the bridge and towards the eastern side of the lock. I could see nothing in the black waters.

The Jesus Lock was efficient, and the water level had begun to drop visibly. I started across the bridge towards the lock controls. The mysterious figure had vanished. I had to stop the flow!

I reached the controls, but just then Holmes surfaced, treading water with mighty strokes as he fought not to go under. He looked wildly about for me.

‘Over here, Holmes! I’ll stop it!’

‘No, Watson! Hold off!’ he shouted. ‘Buttons is caught in the mechanism! I’m going down.’

Before I could respond, he disappeared below the surface. Closing the lock now could trap and crush the two men down there. I was unsure what to do.

A police van and a Black Maria pulled up to the side of the river. I ran to the edge, horrified. ‘Holmes!’ I cried. The water level in the lock had dropped precipitously. A minute had passed since he went under.

By now there were five or six policemen on the scene.

‘Two men in there!’ I shouted.

‘Close down the lock! They’ll be sucked under!’ cried an officer.

‘No! Don’t touch it! One of them is already caught in the mechanism,’ I yelled.

Two brave policemen tore off their boots and coats and dived in. ‘Which side? There are two tunnels!’

I pointed to the one on the south side. But was I sure?

Two minutes. How long had Holmes been under there?

Lightning flashed, and the thunder cracked again. The swimming policemen dived under and resurfaced once, then twice, each time empty handed. Was it the south tunnel? Or had I been mistaken …

Three minutes.

Then, suddenly, I saw them.