Our heroes (probably) return from a night of wenching, drinking and sleeping in Hommlet, to search the cell block for secret passages (since there are no obvious ones). If they follow the blood trail to the secret door in the stone pillar, they'll find a tunnel to an old crypt... with undead! PC:s can never catch a break.
Cliché aside, four ghouls work pretty well as a combat encounter. Their regular claw attack immobilizes the target, which sets it up for a subsequent bite attack which stuns. Obviously, this works better the more ghouls are still alive. When the party has worn down the pack to one remaining ghoul, that one is pretty pathetic. Consider having it try to flee when bloodied.
Also consider moving a treasure parcel here. The module doesn't, but come on. It's a crypt! It should be filled with treasure.
After clearing this room, the characters can go straight to the boss fight, to a dead end, or fight some of the actual underlings of the boss. (So far, only the ogre has been an actual hired goon.)
Next up: The Monster In The Dead-End Room.