The wharf-wall was pierced by an arch whose floor was a noisome back-water of the Thames. The boat of Mr. Bhnh was more or less keeping station before that arch, though the current was flowing one way and the tide striving against it, so they were being ill-used by marauding vortices and pounced upon by rogue waves. The waterman, in other words, was using every drowning-avoidance skill he'd practised in the rocky flows off Qwghlm, and more than earning his pound. For in addition to duelling those currents he had been prosecuting a negotiation with a figure who stood on the top of the wharf, just above the arch. That man in turn was exchanging shouts through a speaking trumpet with a periwigged gentleman up on the parapet of the wall behind: a crenellated medieval sort of affair with a modern cannon poking out through each slot, and each cannon conspicuously manned.