‘And could we still go into them?’ said James. ‘Would we find countless treasures in there that have been concealed from mankind for decades?’

‘Only a couple of streets were covered, I think. Push away there.’

There was a shove from James and Soldier John’s side of the boat, which angled our side towards the houses. We put our oars out, ready to push away from their walls.

‘And I wouldn’t ’ave thought there’d be any treasure. Just a load of old junk. Sea levels didn’t rise suddenly, remember. People ’ad time to get the good stuff out.’

‘But could we go round them if we wanted to? When the tide is out further?’ asked James.

I didn’t like the look of them at all. I didn’t like the idea that people had once lived in these hidden, empty places. Nothing good was down there now. From the few exposed walls and chimneys, the houses looked like resting places for crabs, and seaweed, and mussels. They had been taken back by the sea.

‘More carefully on that side,’ said Soldier John. ‘Lever the oars against the walls to push us forward. An’ you can go round those ’ouses if you want, James, but you’ll be doin’ it by yourself.’

‘Hullo!’ called Dr Jones from the shore. ‘Throw me the rope.’

Lana threw, and the rope landed wetly in the water in front of us.

‘Again.’

There was a shoal of fish in the house we were passing now, following each other in one of those twisting, arcing fish dances. For a minute I thought that they must have got trapped in there during the highest point of the tide and I almost said something beautiful and profound about them being like the reverse of us: sea creatures trapped by mankind. But then I remembered that houses have doors and windows which the fish could swim in and out of if they wanted to, so it was good that I didn’t mention it.

Dr Jones and Stinky pulled on the rope, and we guided ourselves in with the oars.

‘That’s it,’ said Dr Jones. ‘That’s as far as we can get you. You’ll have to walk along the walls.’

She tied the rope loosely round a lamppost.

‘Climb down, kids,’ said Soldier John. ‘’Ave you got enough? Any more?’

Stinky held up two black plastic bags. They were even bulkier than last time. It looked like more people would be escaping on Soldier John’s next trip.

‘Come on,’ said James. ‘Let’s do it!’

We stepped down uncertainly. If the boat surface had felt strange, this was worse. The seaweed on top of the submerged houses was both furry and slippery, but underneath was an uncomfortable hardness. With every step I felt like my foot was stopping too soon, like it should be sinking further into the surface of the wall.