Ah, tributaries! That's what I was meaning to come to. The Churn, the Key, the Ray, the Coln, the Leach, and the Cole: in these upper reaches of the Thames, these are the streams and rivulets that come from elsewhere to add their own volume and momentum to that of the Thames. And tributaries are about to join this story. We might, in the quiet hour before dawn, leave this river and this long night and trace the tributaries back, to see not their beginnings--mysterious unknowable things--but, more simply, what they were doing yesterday.