William "Steamboat Bill" Canfield is the owner and captain of a paddle steamer that has seen better days. He eagerly awaits the arrival of his college student son, whom he has not seen since the lad was a baby. Expecting a big, husky man like himself to help him compete with businessman John James King and his brand new, luxurious riverboat, he is sorely disappointed with his slight, awkward offspring, who shows up with a pencil moustache, a ukulele and a beret. He becomes outraged when he discovers that his son and King's daughter Kitty, also visiting her father, are in love. Both business rivals are determined to break up the relationship.
When Canfield's ship is condemned as unsafe, he accuses King of orchestrating it. He assaults his enemy and is put in jail. His son tries to free him by bringing him a loaf of bread with tools hidden inside, but his scheme is detected. The sheriff hits Canfield Jr. on the head, sending him to the hospital.
Then a cyclone hits, tearing down buildings and endangering the ships. As Canfield Jr. makes his way through the town, a building front falls all around him. He reaches his father's ship and rescues first Kitty (stranded on a floating house), then his father (by ramming the ship into the sinking jail, which has also been blown into the river), and finally Kitty's father. When Kitty goes to her hero, she is puzzled when he jumps into the water. However, his purpose becomes clear when he returns, towing a minister in a lifebuoy.