The Traitor - DM Notes

The party is hired to retrieve a valuable object believed to found in an Ostrangardian ruin. The ruin is what remains of an estate, with a defensive tower. The night before delving into the ruin, there is a sign that one of the party is against them, and potentially hired by a rival.
Ideas: 

• a coded message is intercepted
• premonition?
• warned by their employer
• soup is poisoned

The party is each given snippets of how to access the vault based on research they completed, however, the info is not necessarily correct or complete.
Ideas: