"Mysterious Ways" is a D&D adventure set in the Holy Land (Israel and Jordan) during the time of the Crusades (1114 A.D.) in an alternate-Earth setting. This is a world where the portals to otherworldly realms, particularly the Lower Planes, are closed--sealed shut by the power of the True Cross, a holy relic sought by evil thieves who would see the gates to the Lower Planes flung open. Magic exists in this alternate world, but it is less prevalent than in other D&D campaign settings. This paucity of magic serves the core of the adventure's storyline and should be preserved, if possible. This adventure is designed for a party of four 7th-level player characters (PCs). It is recommended that the party include at least one lawful cleric or paladin. Consult the "Adapting the Adventure" sidebar for ways to incorporate the adventure into generic D&D campaigns and modify it for higher or lower levels of play.