Kermit the Frog acts as the narrator for the tale, which begins when he and the other frogs in the woods gather at a pond near a castle one day. They are surprised to see a new little frog (Robin), who claims to be a prince known as Sir Robin the Brave. He explains how he became a frog: As a human (Gordon Thomson) he came upon an ogre (Sweetums) who tried to attack him with a club. Just as Sir Robin was about to strike the final blow, a witch appeared and turned Sir Robin into the frog. After learning that he can only break the spell by befriending and kissing a princess, Robin escapes being eaten by Sweetums.
The other frogs do not believe this tale, though Kermit still welcomes Robin to their midst. Upon learning of the castle nearby and the princess Melora (Trudy Young) who lives there, Robin becomes determined to befriend and kiss her to break the spell. He soon learns that she too is under a curse, so that everything she says is mixed up so that no one can understand her. While sitting by the pool, she drops her ball into the water and Robin retrieves it, despite the fact that he cannot swim. As a reward, Melora agrees to take him to live with her in the castle as a friend. Robin soon learns that the witch who cursed him was also responsible for the curse on Melora, so that the princess will not tell her father the truth (the witch tricked the king into believing she was his long-lost sister Taminella). The princess seems to know the witch's one weakness, "bake the hall in the candle of her brain", however no one is able to decipher the sentence to know what it truly means.
The witch recognizes Robin and kidnaps him to feed him to Sweetums, however Kermit rescues Robin. They learn that the witch managed to convince the king that because of the curse, Melora is unfit to be next in line for the throne and therefore the king decides to coronate Taminella as the new queen. Kermit and the other frogs disrupt the coronation and Robin is able to figure out how to stop the witch's power - break the ball on the handle of her cane - which turns Taminella into a bird.
With the witch gone, the curse on Melora is lifted. As thanks, the princess kisses Robin, lifting the curse on him as well. Sir Robin declares his love for Melora and Melora is coronated as Queen Melora I. Kermit concludes the tale by telling the audience that the two were married and had a child, Prince Kermit.