The largest daily transport operation in the world - that which links the fishermen who land their catch at Hull and elsewhere with Britain's 30,000 retail fishmongers. The trawlers, the drifters, the little inshore boats; the clatter of the quayside and the 'mystery' of the fish auction: the icing, the filleting, the washing, the boxing; the trains criss-crossing through the night; and Billingsgate, a fish market as old as the Writ of Domesday.