This quest is relatively short, but has great rewards. It is recommended to do this quest immediately after completing the Tenochtitlan quest, but take note that the fights here only look deceptively simple.
Go to Caracas and there is a chance that a crowd has gathered outside the tavern. Talk to one of them and they will tell you that a werewolf is inside.
Enter the tavern and speak to the owner about the werewolf. Go upstairs and have a chat with the "werewolf". It turns out that the "werewolf" is actually a person who came from Maracaibo but fled due to a mysterious curse. He asks you to help him lift the curse. Agree.
Go to the church and speak to the priest about the man and the curse. He will request that you bring the man to the church so he can take a good look at him. Head back to the tavern and talk to the tavern owner. You will find out that the man has been taken away by the mob and burned. There is nothing for you to do here anymore; sail to Maracaibo and talk to the tavern owner there to learn more about the curse. He will mention that he has not seen any of the fishermen from Des Moines for a while now.
Des Moines can be found behind the Cape of Unfulfilled Hope. Go there during the night (or nothing will happen later on) and a sentry will greet you. Kill him and his crew and enter the fishing village. You will find out that the inhabitants are all skeletons. Go inside one of the houses and speak to the leader, Fernando Torres (yes, just like the footballer) and he will tell you that a mysterious curse has been plaguing their village, turning them all into undead during the night (gee, just like the Pirates of the Caribbean movie...). Apparently, it started when a brig named "Queen" laid anchor near Des Moines. The pirates had a dispute and things got out of hand. Ever since then, the curse has been plaguing their village. Later on, an Englishwoman named Elisabeth Sheppard came asking about the Queen and so you offer to find this woman for them as she may have some clues on how to break the curse.
You can find her in Charlestown. The leftmost house near the sea is her home. Talk to her and you will learn that she is the daughter of a famous pirate captain and that she was visited by a skeleton some time ago, which she postulates who she knew and might be the key to breaking the curse. Now, in order to lift the curse, you will require the Jade Skull of Mictlantecuhtli, the Aztec god of the kingdom of the dead. In order to get it, you will need to finish the Tenochtitlan quest. Be warned however; it is not an easy quest (unless you're level 45+), and can take quite a long time to do (without cheats).
Now, when you have the Jade Skull, go back and talk to Elisabeth Sheppard. She will tell you to look for a brig named "Queen". From here on out, go out into the world map and sail around (you should preferably leave one ship slot free so you can capture the "Queen" later). You will eventually meet a ship with purple sails on the world map - this is the brig "Queen", and it is NOT an easy ship to fight. Save before engaging her in combat. The brig "Queen" is alone, but she is fast and maneuverable, and the worst thing is that she is commandeered by a very good captain with 90+ in ship skills. This means she will land a lot of hits on you because she is impossibly accurate, and she also has a high chance to deal critical hits to your ship. This may cause problems for you if your ships are only Class 4 ships and above.
Now, you don't want to destroy the ship. Rather, you want to lift the curse and to do so, you will need to board the ship. So get close to her, board her, and fight your way to the captain's cabin. There, you will meet Danielle Sheppard who will fight you, and when you defeat her, she will ask why you have boarded her ship. Tell her that Elisabeth sent you and that the curse has been lifted due to the help of the Jade Skull and she will be immensely grateful, accepting your offer to join your crew as a female quest officer.
Congratulations! You're now in possession of a unique brig called "Queen", and the best quest-officer in the game, Danielle Sheppard, who has crazy stats and 90+ in nearly all ship skills and luck, making her an invaluable asset as a second ship commander. In ship combat, you can either give her a fast ship and watch as she outmaneuvers her opponents and blast them out of the water, or give her a huge battleship and she will fire with crazy accuracy and blow them out of the water anyway...so...you really can't go wrong with her in your squad.
Anyway, now that you've lifted the curse, return to Des Moines to collect your reward. You can either accept the 100,000 pieces of eight as a reward or refuse it to gain quite a bit of reputation points.