From the Introduction:
This mini-module has been designed for a group of 4-7 characters of 4th to 6th levels of experience. It requires information only found in the AD&D game rules, and cannot be played without them.
The inspiration for this scenario comes from the legends of the Celtic people. However, it is not intended to be a reconstruction of any particular story from that mythos, nor is it intended to be an adventure set in any historical context. The scenario has been designed to allow the DM to introduce a Celtic feel into play. Therefore it is possible for players to use characters who have not existed in this kind of background before, but who have taken up residence in the lands of Conall mac Éogan.