The Trumpet of the Swan is a coming-of-age novel in the bildungsroman tradition. It follows the main character, Louis, who happens to be a trumpeter swan born without a voice. Over the course of the book, Louis receives the gift of a trumpet from his father, who stole the instrument hoping it could serve as a substitute for Louis's voice. The young swan is also befriended by Sam, a boy who takes Louis to school where he learns to read and write. By writing on his chalkboard, Louis learns to communicate with human beings. As a young adult swan, Louis has two goals: to earn back enough money to pay for the stolen trumpet, and to win the love of Serena, a stunningly beautiful female swan.
White creates the suspension of disbelief gradually. First, he endows the swans with the ability to not only speak to one another, but to understand the speech of human beings. Next, he displays Louis's parents, particularly his father "the cob" behaving in a very anthropomorphized fashion: stealing a musical instrument that is physically impossible for a bird to play, and expressing guilt for having stolen the instrument instead of paying for it. From this point, Louis develops more and more human traits. He learns to read and write. He gets a job playing the trumpet, and he even spends the night in a fancy hotel where he orders watercress sandwiches. He even comes up with a plan to musically impress the exhausted Serena, who splashes down at a zoo where Louis is staying. Seen individually, most of Louis's later exploits appear ridiculous. Yet in the story, if the reader accepts the author's first few fanciful notions such as swans that understand human speech, the successively non-animalistic behavior of the main character becomes just as plausible as the actions of the rabbits in Watership Down.
Like most books written for children, The Trumpet of the Swan emphasizes the words and actions of its characters and focuses relatively little on their inner workings. The swans do experience very human emotions, such as remorse and love. The lifelong bond between Louis's parents, like Louis's bond with Serena, is part of the story that has a basis in fact: trumpeter swans do indeed mate for life. They also migrate, and the migration of Louis's family is one of the things that influences the development of the story. Louis's decision to visit Sam instead of joining the family during their migration to Montana signals his separation from his family and also from greater swan culture. Although he communicates well with people, he still cannot communicate with other swans because swans can't read. The cob therefore decides to provide Louis with a trumpet, and steals it from a music store.
While spending the summer with Sam instead of returning north with his family, Louis teaches himself to play the trumpet. This is a biologically ridiculous notion: trumpets make noise only when someone vibrates his or her lips against the mouthpiece while moving enough air through the instrument to make it resonate at a given pitch. Although it is plausible that a swan's three webbed toes could press the three valves of the instrument if the webbing between the toes were cut, the idea of a bird creating an adequate embouchure for the instrument is quite silly: birds simply don't have lips. Most readers, lacking the particular knowledge of how to play a trumpet or bugle, will overlook the problem. Indeed, for a swan to learn popular tunes like "Beautiful Dreamer", even by ear, is not a huge stretch for a reader who has already accepted the notion that a bird can learn to read and write. Similarly, when Louis telegrams Sam--who would have been no more than twelve or thirteen years old at the time--and asks him to journey across several states to Philadelphia, nobody in the story offers anything resembling a serious objection.
Unlike most books written with animal characters that talk, The Trumpet of the Swan violates a very common "rule" that applies to both authors and movie-makers: when animals speak to one another, there are seldom or never any human characters who speak, and if humans speak they and the animals are not mutually intelligible. By allowing Louis to learn to read and write, White opens up the possibility of candid interspecies communication. Louis's writing is not a performance trick, after all: he really does have things he wants to communicate. But the first swan with whom Louis communicates is Serena, and he does it with the universal language of music.
Once Louis achieves his goals, he retires from human society to live entirely as a swan, giving up his money pouch and his writing slate.
Aside from Louis, and to a lesser extent his father, most of the characters in the novel are quite flat. There is no real antagonist, and the only serious antagonisms in the book stem more from misunderstandings or conflicts of interest than from actual malice. This is consistent with White's other books, Stuart Little and Charlotte's Web. However whereas Charlotte's Web in particular featured several different kinds of characters with distinctive traits and voices, The Trumpet of the Swan really only has two unique characters: the introverted Louis and his flamboyant but good-natured father, the cob. The human characters almost always interact with Louis in a simplistic but positive way.
