From the website:When the dreaded black rain falls, all those who revere deities or rely on them for power and protection cringe in fear. The black rain forms a wall between the mortal and the divine and thus, when it falls, clerics lose all ability to cast spells and work miracles. Only the foulest of villains would use this opportunity to strike against the near-helpless clerics of an otherwise powerful temple.When the black rain falls, the temple of St. Cuthbert comes under siege and a magical barrier prevents anyone from helping the beleaguered clerics and temple defenders inside. Someone has to find a way to aid them, and quick!Black Rain, April's free online mini-module by Call of Cthulhu d20 RPG designer Monte Cook invites your 16th-level characters to challenge an insidious plot for revenge against the temple. - BoardGameGeek