This is a new mission in the Samhain 2013 event. It's a side mission started next to Danny in Kingsmouth Town. This mission is listed as completed under Savage Coast. This mission awards you with Sam's spooky story which is one of the 10 stories needed to complete the Spooky Stories of Solomon Island mission.
A note by Danny seems to indicate that he is searching for a very rare story for his collection. Track down the rare story.
Reward: 74,800 XP, Sam's spooky story, 10,000 Pax Romana, Sack of Penny Dreadfuls
This mission refers to Sam Krieg's biggest fan, which is a from the mission Crime and Punishment - click the link for the mission guide, which is filled with spoilers. The passwords are the same.
SPOILER: The code for the mancave is 8237.
Inside the basement look for the strong box. The code for the strong box is new. This is also where Lore #10 is located.
HINT: The code is on the fan blog for Sam Krieg.
HINT 2: Check for the book you are looking for.
SPOILER: The code is 5731.