Fight through three decks full of Spectral Sailors to find Varulae's Crystal Ball. The inside of the ship is a pretty confined space with little room to bob and weave. If the Hero's fighting style favors dodging and is having trouble slugging it out toe to toe with the sailors, they will follow the Hero up on deck. This will get some more room and also bring a few of NPCs to distract them.
There will also be a random magic piece of jewelery, 100 in the Captain's Chest, and some Skooma and jewels on the bottom deck. With a high enough Sneak skill and using chameleon, the Hero can sneak through the entire ship without being detected.
A High Elf Sorceress named Varulae has asked me to retrieve her crystal ball, located in the hold of the ship the Serpent's Wake, which is moored up in Anvil Bay. The crystal ball is in a chest in the ship's hold. I should be careful, however -- the crew have all been slain, and now roam the ship's decks as creatures of undeath.
I have retrieved Varulae's crystal ball. I must now return it to her on the top deck of the Serpent's Wake
I have given Varulae her crystal ball. She gave me the captain's enchanted cutlass as a reward.
- A note discovered inside the ship refers to the ship's crew calling a certain person in Anvil a "human rat", being the man that lives in the basement of the lighthouse.
- The reason for the sailors' deaths can be found in the Traitor's Diary during the Dark Brotherhood quest "Following a Lead."