Written by Old Bluffer 8th Jan 2007

Kindly written in a stream of conciousness by Mr. Briggs Inc. (fullstops added by Old Bluffer)

Muska is a government agent from an evil nation who wants to become the new king of the long deserted eponymous floating fortress.
Sheeta, a young girl who is the true heir to this throne, holds the secret of how to control the floating citadel in the form of a magical stone, given to her as a child.
The poor girl then spends the whole film being chased by Muska and his minions.
In the final climax, both her and a young boy, Pazu, have made it to Laputa, but Muska apprehends them before they can take control.
She passes the magical stone to Pazu (with whom she will surely end up as more than just a good friend if they survive...) and he is forced to run off to safety.

"How appropriate that we've ended up in the throne room." says Muska.
"This is no longer a throne room. This is a tomb for the both of us." replies Sheeta. "You see, a king without compassion does not deserve a kingdom. You will never possess the crystal! You and I will die here, together."

She then says she understands why the people of Laputa vanished and explains why, in the form of a somewhat confusing song from her home town, Gondoa;
"Take root in the ground, live in harmony with the wind, plant your seeds in the Winter, and rejoice with the birds in the coming of Spring."
She goes on to say that love is essential no matter how many weapons you have. (I still don't know how the song applies!) [It probably lost something in the translation! - Old Bluffer]

Shooting off both her pigtails, and threatening her ears next, Muska says that Laputa will return to life and demands that he get his stone back. Just then Pazu emerges into the room with a large gun he can barely lift that the friendly pirate, Dola gave him. He says that he has hidden the stone and that if he hurts Sheeta, he'll never get it back. He then negotiates a minute to talk privately with Sheeta.

Pazu then explains their only hope is for her to recite the spell of destruction her grandmother taught her long ago. The two join hands around the crystal and recite the chant "Balus".

The power core at the center of Laputa then shoots fire out from its orbit inside the Laputian control room and causes the entire castle to fall apart around the trio. Pazu and Sheeta take off to make their escape as Muska is blinded by the illumination radiating off of the Laputian power core. He is last seen staggering down a crumbling hallway of the quaking castle in the sky.

Submitter Note
He is one of the few Hayao Miyazaki villains who gets his just desserts, probably because he is one of the few who doesn't have a "good side," still, his fate remains uncertain since we don't visibly see his demise, but we can assume that if he wasn't crushed by one of the loose falling stones, he surely fell to his death to the ground below.