Ghost Brothers Achievement
Make sure Max and Sam get home in time for tea.
First you must complete the "Bored to Death" quest in Mourningwood.
Quest: Gone But Not Forgotten
Worth: 10 Guild Seals
Location: Mourningwood Cemetery
How to Complete: You need to help Sam track down his brother. From here Follow Sam and you'll end up at a Crypt in an area called Ossuary. Max will keep running away and you'll just have to follow and fight your way to him.
You'll come to the last area when Max starts playing the organ. Sam will then join him and you'll need to fight waves of enemies until all the wisps around the Normanonomicon (book) have gone. Once it’s clear, run over to it and pick it up and the achievement is yours.
Note: The final stage is a good place to rack up kills. Keep getting caught in the spotlights to summon around 5-6 Hollow Men at once as well as the Ghosts and you'll get a fair few kills. This fight is long so try it as many times as possible before you kill all the Ghosts!