You've arranged to meet your partner in the nearby town of Dunderhaven, but when you get there you learn that they arrived early, tried to burglarize the local castle to get a bit of cash, and haven't been seen since.
You make your way to the castle to look for your partner, but inside are ambushed by bowmen under the command of the brutish castle lord. "Well, boys," he sneers, "another thief. I guess we'll send the scoundrel to meet the first."
He pulls a lever, a trap door opens, and you find yourself dropping down a shaft into the dark tunnels below the castle.