One spring day in Canada, a cob and pen build their nest upon a minuscule island in a pond. Sam Beaver is a nature loving 11 year old boy who observes the pair. At first, they are wary of him for fear he will throw sticks and stones at them but after he saves them from a hungry fox, they begin to trust him. He gets to witness the hatching of the eggs and meet the cygnets. All the cygnets but one "beep" at him in greeting. The youngest is unable to and instead tugs at Sam's shoelace.
The youngest cygnet, Louis, is the subject of his parents' concern as they notice how he still does not make sound as time goes by. They fret about how he may be unable to communicate, much less find a mate. The father has a talk with Louis, where it is confirmed Louis is indeed mute. At first, Louis is distressed because he doesn't want to stick out from other swans but his father is supportive which helps him feel better.
The swans fly south to the Red Rock Lakes in Montana at the end of the summer. Not long after they arrive, however, Louis returns to Canada so that he can learn to "talk" through reading and writing. Sam agrees to take him to school with him. The teacher is cynical at the beginning but Louis is a fast learner. Sam buys him a chalkboard with chalk for him as a gift.
Because the other swans cannot read and write, Louis' failed attempts at communication leave him as lonely as ever. In addition to this, he is unable to communicate with is love interest and so she ignores him. Seeing his son miserable inspires Louis' father to fly to Billings where he crashes into a music store window and steals a trumpet for Louis. Although Louis accepts it, he feels guilty about the trumpet being stolen.
After Louis tells him about this situation, Sam suggests Louis get a job to pay off the cost of the trumpet and the damage done to the store window and helps Louis get a job as camp bugler at Camp Kookooskoos which Sam also works at. Louis learns to play taps, mess call, reveille, and even composes a song for his beloved Serena. He has Sam split one of his feet with a razor blade to form digits to play properly with.
Applegate Skinner is a camper who goes out into the lake after getting made fun of and feeling bitter. He nearly drowns because of his inability to seim until Louis rescues him. Louis is awarded a medal and receives his pay along with a waterproof moneybag. At Sam's suggestion, he moves on to Boston to try and get a job with the Swan Boats. He becomes a sensation and even gets to stay at the Ritz Hotel.
Abe "Lucky" Lucas offers Louis a job at a Philadelphia nightclub which pays more than his previous job in Boston. He accepts the offer and stays at the zoo, where arrangements have been made for him to stay and not be pinioned. One particularly windy night causes Serena to be blown off course and she winds up at the zoo Louis happens to be staying at. Louis plays his trumpet for her and finally winds her heart. The rejoicing is cut short when zookeepers try to clip her wings so she will remain at the zoo. Louis fights them off and they are unsuccessful in their attempt.
Louis persuades the Head Man to temporarily put off clipping Serena's wings. Meanwhile, he sends Sam a telegram in which he asks for his help. Sam flies to Philadelphia and visits the zoo. He successfully convinces the Head Man to strike a deal with him and Louis: the two swans will be allowed freedom as long as the zoo gets to keep a cygnet every now and then.
The two swans fly to Red Rock Lakes. Louis writes an apology to the storekeeper on the slate and his father flies to Billings with the slate and money to deliver it. The storekeeper shoots the cob out of fear that he will try to steal something again. He realizes his error after seeing the note on the board and moneybag. A hullabaloo ensues and he gets into a quarrel with a police man and warden about who gets to keep the money. Louis' father is taken away to a hospital as a judge who happens to be in the crowd that formed decides who gets the money.
The judge decides the shopkeeper is allowed to keep it and the man chooses to donate leftover money to the Audubon Society. Louis' father recovers successfully and returns to the Red Rock Lakes. In the spring, Louis and Serena flew north to start a family.
It is summer and Sam is now about 20. In the conversation he has with his father, he mentions that he has not talked to Louis in a while since Louis has no money and therefore cannot buy stamps and write. Sam actually knows the swans still live at the pond nearby but keeps that a secret. That night, Sam hears Louis playing his trumpet and writes about it in his journal, saying that there is nothing in the world he likes more than that sound.
