The stairway down the catacombs is inside the church, and locked. Only Father Samael can open the door with his key. He locks the door behind them, and tells the characters to knock twice in patterns of four to let him know it is them.
As the party explores the catacombs, they are hunted by the Snatcher.
Each time a character goes down a corridor, roll a d4. On a 1 or 2, the monster appears at the opposite end and gives chase.