Is there a plot? Is there ever! One might even say there are several. Let's see how succinct I can be...
Captain Ben Avery, RN, is charged with delivering a fantastic jewel encrusted crown to the King of Madagascar. The ship he is sailing on is captured by the Brotherhood of the Coast, out to save their comrade, Sheba the She-Wolf from being transported as a slave (Sheba is captured in the fort raid the opens the story). The Brotherhood divides the crown into six pieces, for the six captains to sell. They also kidnap Avery's beloved, Lady Vanity, for sale in the Basra slave marts by corsair captain Akbar the Damned. Avery, assisted (and sometimes hindered) by anti-hero Thomas Blood, must regain the pieces of the crown, rescue Lady Vanity, defeat the Coast Brotherhood, and give general what-for to the forces of the evil Spanish Viceroy Don Lardo del Baloona de Lobby y Corridor.
That's it in a very small nutshell. The whole thing is pretty packed with incident. Not to mention plenty of killer fights, ship battles, swinging on ropes, beautiful women, giant octopuses, marooning; you name it.
Then, there's all the stuff we had to leave out--the Lost City, a retired Anne Bonny, the dreaded maguay plant. I really can't reccomend the novel the play is based on enough. Its a satire, and packed with utterly ridiculous anachronisms, but its meticuloulsly researched, and carries the spirit of the words of Sabatini. Even if you can't see the play, do youself a favor and read the book, damn me deadlights!