The three friends – George, Harris, and narrator J. – go on a boating trip along the River Thames in England. Heading upriver, they pass every town between Kingston and Oxford, and leave the boat on occasion. Heading back downriver, they leave the boat at Pangbourne, which lies between Streatley and Maple-durham, and take the train back to London.
J. and Harris begin the expedition at Kingston, then have lunch at Kempton Park. They pick up George at Weybridge. They spend the first night tied up at “Picnic Point,” somewhere past Staines. The second day, they go to Magna Carta Island, have lunch below Monkey Island, and spend the night in Marlow at the “Crown.” In Marlow, on the third day, Montmorency has an encounter with a cat. The men also go grocery shopping here. They get back in the boat and have lunch near Wargrave. At Sonning, they get out and walk around the village. They spend the night on one of the Shiplake islands. George and J. go to Henley after supper. On the fourth day, they pass Reading. They spend two days in Streatley and get their clothes washed here. George and J. go to an inn and hear the stories about a mounted trout on display. The next night has them in Culham. Then they proceed on to Oxford, where they spend two days. They begin their return trip downriver, but it rains for two days, and everything is wet. They leave the Thames at Pangbourne.
A link below provides a general map of the river and its larger towns. You can see Kingston and Oxford, and some of the other points mentioned in the book. Not all of them are large enough to be shown on this map.