The story begins by introducing George, Harris, Jerome and Montmorency, a fox terrier. The men are spending an evening in J.'s room, smoking and discussingillnessesthey fancy they suffer from. They conclude they are all suffering from 'overwork' and need a holiday. A stay in the country and a sea trip are both considered, then rejected after J. describes the bad experiences had by his brother-in-law and a friend on sea trips. The three decide on a boating holiday up theRiver Thames, fromKingston upon ThamestoOxford, during which they will camp, notwithstanding Jerome's anecdotes about previous experiences with tents and camping stoves.
They set off the following Saturday. George must go to work that morning ("George goes to sleep at a bank from ten to four each day, except Saturdays, when they wake him up and put him outside at two"), so J. and Harris make their way to Kingston by train. They are unable to find the correct train atWaterloo Station(the station's confusing layout was a well-known theme of Victorian comedy) so they bribe a train driver to take his train to Kingston, where they collect the hired boat and start the journey. They meet George up-river atWeybridge.
The remainder of the story describes their river journey and the incidents that occur. The book's original purpose as a guidebook is apparent as J., the narrator, describes passing landmarks and villages such asHampton Court Palace,Hampton Church,Monkey Island,Magna Carta IslandandMarlow, and muses on historical associations of these places. However, he frequently digresses into humorous anecdotes that range from the unreliability ofbarometersfor weather forecasting to the difficulties encountered when learning to play theScottish bagpipe. The most frequent topics of J's anecdotes are river pastimes such as fishing and boating and the difficulties they presented to those who were inexperienced and unwary and to the three men on previous boating trips.
The book includes classic comedy set-pieces, such as the story of two drunken men who slide into the same bed in the dark, theplaster of paristrout in chapter 17 and the "Irish stew" in chapter 14 made by mixing most of the leftovers in the party's foodhamper:
I forget the other ingredients, but I know nothing was wasted; and I remember that, towards the end, Montmorency, who had evinced great interest in the proceedings throughout, strolled away with an earnest and thoughtful air, reappearing, a few minutes afterwards, with a dead water-rat in his mouth, which he evidently wished to present as his contribution to the dinner; whether in a sarcastic spirit, or with a genuine desire to assist, I cannot say.