From publisher blurb:
Crypt of the Shadow Lord is written for one, first-level, lawful cleric. With little to no adjustment, the Basic Rules from other, similar Fantasy Role Playing Games may also be employed successfully. Although designed as a solitaire, this adventure also plays well as a duet (one player and one referee), and is intended as something of an introduction for both novice players and game referees.
Not unlike the "choose-your-own-path" books of yesteryear, this adventure has been written so that the storybook (along with some assistance from you) plays the role of referee. The crypt offers numerous ways for a first-level character to meet their doom, however, if the adventure is completed successfully, there is an excellent chance that they will have won enough XP to advance a level.