'What _can_ there be?' said Davies.

'What about that dyke?' I said, with a sudden inspiration.

From the bank we could see all along the coast-line, which is dyked
continuously, as I have already said. The dyke was here a substantial
brick-faced embankment, very similar, though on a smaller scale, to
that which had bordered the Elbe near Cuxhaven, and over whose summit
we had seen the snouts of guns.

'I say, Davies,' I said, 'do you think this coast could be invaded?
Along here, I mean, behind these islands?'

Davies shook his head. 'I've thought of that,' he said. 'There's
nothing in it. It's just the very last place on earth where a landing
would be possible. No transport could get nearer than where the Blitz
is lying, four miles out.'

'Well, you say every inch of this coast is important?'

'Yes, but it's the _water_ I mean.'

'Well, I want to see that dyke. Let's walk along it.'

My mushroom theory died directly I set foot on it. It was the most
innocent structure in the world--like a thousand others in Essex and
Holland--topped by a narrow path, where we walked in single file with
arms akimbo to keep our balance in the gusts of wind. Below us lay
the sands on one side and rank fens on the other, interspersed with