Note that it bears little resemblance to the Disney version -- both are loose adaptations of the same Hans Christian Andersen fairy tale, but with different goals; the animated version to appeal to children, of course, and this version to give it an explicit Christian theme.
It's Princess Jewel's sixteenth birthday; her coming-of-age. To mark the occasion, she is to join the Siren chorus and go to the surface for the first time, to use her singing to entice a human sailor into giving up his soul (Siren Song). This is what mermaids do, and having lured many sailors to their doom in this way is a mark of status in the undersea world. The sailors live on under the sea, but without souls, and thus without hope of life after death. One such unfortunate is Nicodemus, Jewel's tutor, who has filled her head with stories about the human world and about the immortal soul that humans have, but which mermaids and their captured sailors lack.
Upon going to the surface, the first human Jewel sees is the dashing Prince Christian. She hears him singing about his adventurous life and, above all, his strong faith in God (I Am Complete). She is immediately fascinated and forgets what she's supposed to be doing, enraging Crustacea (the choir-mistress), who conjures up a squall that knocks Christian overboard. Jewel rescues him and takes him to shore, singing to the unconscious man about the strange new feelings she's experiencing (Quandary), but she hides as soon as she hears someone coming.
Princess Sapphire, a human princess, finds Christian there on the beach, and takes him back to her castle to nurse him back to health. The two of them discover that they share their faith in God, and fall in love (He Brought Me To You). But Jewel overhears Christian referring to Sapphire as "my sweet jewel" and think's he's talking about her, and becomes determined to find a way to be together with him.
Crustacea learns of this and plots to use it to get rid of Jewel, against whom she bears a grudge because years ago, King Argo turned her down to marry Jewel's mother (Crustacea's sister, in fact). She has Nicodemus killed, since he's the only one who would be able to talk sense into Jewel, and then offers to turn Jewel into a human so she can go to Christian. Jewel accepts the offer and is transformed, in exchange for her voice, and on the condition that if she touches seawater again she'll die (The Transformation).
Meanwhile, Prince Christian leaves for home to prepare for his forthcoming wedding to Princess Sapphire. Sapphire bids farewell at the dock (The Gift). On the way home, his ship runs across a beautiful mute girl floating in the sea. They take her aboard, and she soon becomes the darling of the entire crew (Her Silent Song). Christian, however, sees her as nothing but a friend, since he's still totally in love with Sapphire (Duet For One).
Jewel's fellow sirens come up to the ship and tell her that she can still turn back into a mermaid, if she kills Christian. Jewel refuses. Crustacea and King Argo both show up, and Crustacea first attacks Argo, and then the ship. In the battle, Christian is thrown overboard, but Jewel jumps into the sea and rescues him, then dissolves into foam (The Battle / Epilogue). As a reward for her selfless actions, she is given a soul, and reunited in heaven with Nicodemus (Finale).
(Five songs that didn't really relate to the main love-triangle storyline have not been included)
I Am Complete
He Brought Me To You
Her Silent Song
Duet For One
The Battle / Epilogue (This one hosted on a different site because it repeatedly broke YouSendIt.com >_<)
Personally, I think the best thing about this musical is how astonishingly likable Princess Sapphire is. In the original story, the princess that the prince marries has only a few lines about her, so the readers know her only by her function in the story--that is, to break up the prince and the mermaid--and so we dislike her. But in this version, we get to know Sapphire very well; she has as many scenes with Christian as Jewel does, and seems like a wonderful person and a perfect match for him.
So the ending of the story isn't tragic at all, since everyone is right where they should be--Christian is with Sapphire, both of them blissfully complete in their love for God and each other, and Jewel is in heaven with God, having been led to Him by Christian. Christian was never intended to love Jewel...rather, it was (presumably) God's plan that Jewel, through her love for Christian, would discover the path to His love.
To my f-list: feel free to link to this post! There are 20 downloads on these songs, and there's no way they'll all be used up if they're languishing on this little out-of-the way journal. Share the musical love, people! XD