This is the second Eamon adventure and the first outing not explicitly meant for beginners. It was released probably in late 1979, with or shortly after the debut of the Eamon system itself, and is the first to include features such as buried items and locked doors.
You've arranged to meet your girlfriend Larcenous Lil (or in the case of a female adventurer, your boyfriend Slippery Sven) in the town of Dunderhaven. When you get to town you learn that Lil, who arrived before you flat broke, tried to get some cash by burglarizing a nearby castle and hasn't been seen since.
You go to the castle after her, but once inside you're ambushed by bowmen under the command an ugly man on a throne who takes you for another thief and casts you down a shaft to meet the same fate as Lil. After a long drop and a "thud", you find yourself unhurt but with no way to climb back up the shaft, and so must venture into the tunnels beneath the castle.
Source: Eamon Wiki.