The story is told in medias res as a series of flashbacks. Max Tooney, a musician, enters a secondhand music shop just before closing time, broke and badly in need of money. He has only a Conn trumpet, which he sells for less than he had hoped. Clearly torn at parting from his prized possession, he asks to play it one last time. The shopkeeper agrees, and as the musician plays, the shopkeeper immediately recognizes the song from a broken record matrix he found inside a recently acquired secondhand piano. He asks who the piece is by, and Max tells him the story of 1900.
1900 was found abandoned on the four stacker oceanliner SS Virginian, a baby in a box, and likely the son of poor immigrants from steerage. Danny, a coal-man from the boiler room, is determined to raise the boy as his own. He names the boy Danny Boodman T. D. Lemon 1900 (a combination of his own name, an advertisement found on the box and the year he was born) and hides him from the ship's officers. Sadly, a few years later, Danny is killed in a workplace accident, and 1900 is forced to survive aboard the Virginian as an orphan. For many years, he travels back and forth across the Atlantic, keeping a low profile.
The boy shows a particular gift for music and eventually grows up and joins the ship's orchestra. He befriends Max in 1927, but never leaves the vessel. Apparently, the outside world is too "big" for his imagination at this point. But he stays current with outside musical trends as passengers explain to him a new music trend or style, and he immediately picks it up and starts playing it for them.
His reputation as a pianist is so renowned that Jelly Roll Morton, of New Orleans jazz fame, on hearing of 1900's skill comes aboard to challenge him to a piano duel. After hearing Jelly Roll Morton's first tune 1900 plays a piece so simple and well known ("Silent Night") that the self-proclaimed inventor of jazz feels mocked. As Morton becomes more determined to display his talent, he plays an impressive tune ("The Crave") that brings tears to 1900's eyes. 1900 calmly sits down at the piano and plays from memory the entire tune that Morton had just played. 1900's playing fails to impress the crowd until he plays an original piece ("Enduring Movement") of such virtuosity that the metal piano strings become hot enough for 1900 to light a cigarette. He hands it to Morton, who has lost the duel.
A record producer, having heard of 1900's prowess, brings a primitive recording apparatus aboard and cuts a demo record of a 1900 original composition. The recorded music is created by 1900 as he gazes at a woman (The Girl) who has just boarded and whom he finds attractive. When 1900 hears the recording, he takes the master, offended at the prospect of anyone hearing the music without his having performed it live. He then tries to give the master to The Girl who inspired it, but is unable to and breaks the matrix into pieces.
The story flashes back to the mid-1940s periodically, as we see Max (who leaves the ship's orchestra in 1933) trying to lure 1900 out of the now-deserted hull of the ship. Having served as a hospital ship and transport in World War II, she is scheduled to be scuttled and sunk far offshore. Max manages to get aboard the ship with the recording 1900 made long ago and plays it, hoping to attract 1900's attention. When it does, Max attempts to convince 1900 to leave the ship. But he is too daunted by the size of the world. And feeling that his fate is tied to the ship, 1900 cannot bring himself to leave the only home he has known. Max feels useless that he couldn't save his friend.
The shopkeeper asks Max how the record got into the secondhand piano. Max indicates that he put it there, and the shopkeeper tells him that he wasn't so useless after all. Then, as Max is leaving the store, the shopkeeper gives him the trumpet and says, "A good story is worth more than an old trumpet," and Max walks out as another customer walks in.
The Legend of 1900 received mixed critical reviews. Based on 35 reviews, the film has a 54% rating on review aggregator website Rotten Tomatoes. On Metacritic, the film has a 58/100 rating based on 28 critics, indicating "mixed or average reviews".
Currently the film is rated 8,1 out of 10 on Imdb.