The mood of Three Men in a Boat is in general lighthearted and chaotic, influenced by the unpredictable and often silly events of the plot. After some hilariously persnickety packing choices, and a lot of chaotic fumbling at the notoriously confusing Waterloo train station, the reader is soothed into deep relaxation by the serene beginning of the river journey. On the Thames the protagonists are at leisure, and the reader is too.
However, as the story progresses, the chaos begins to creep back in. It’s driven by the characters' comical mishaps, which leave the reader in disbelief of George’s, Harris’s, and J.’s bungled efforts to take care of themselves. They can’t seem to get anything completely right, including relaxing: for example, when they try to open a can of pineapple, it causes a nasty injury and they end up flattening it. When they decide to pool the remainder of their food to make an “Irish Stew,” they make simple cooking tasks into an exercise in futility. J. peels a potato until all that’s left is a peanut-sized lump. He also drops whole, unshelled eggs into the “stew,” as Harris assures him they will “thicken” it. One would expect their efforts to turn out a ghastly, inedible mess, but the cheerful mood of the novel prevails. J. admits the stew is “a great success,” although “a little too rich for a weak stomach.” By the end of the novel—and after a lot of antics like these—the reader is waiting for the inevitable buffoonery that comes with the men’s attempts to complete serious tasks.
The mood takes another turn towards the end of the novel, becoming more reflective and a little more somber in places. The characters' encounter with the floating dead woman at Pangbourne is an abrupt change, as Jerome invites the reader to think about how common the “old, vulgar” tragedy of a pregnant and abandoned woman had been in the past. While England’s countryside is beautiful, not all of its stories are as lovely as the Thames in spring. However, by the book’s final pages the mood has returned to its previous good-natured silliness. As in the beginning, the “three men” gather around another small table and complain about their imaginary ailments.