From the back of the book:
The exorcist is a protector and guardian against the influence of supernatural creatures upon mortals. He focuses the power of his faith towards rooting out the monsters that would prey on common folk, toying minds and bodies with their unholy powers of domination and possession. He is an expert on rituals that protect people and places from these creatures, and his faith and conviction allow him to detect the traces of their passing in order to expel them back from whence they came.
This is the third book of the Power Class series from Mongoose Publishing. Designed to be seamlessly slotted into any fantasy-based d20 system game, each of these mini-supplements introduce an entirely new core character class, adding a whole new dimension to campaigns. Players will find full details on how to use the new character class, greatly increasing the wealth of options they are presented with by the core rules, while Games Masters may revel in the wide variety of new classes they have at their disposal for non-player characters in their campaigns. Each Power Class booklet can provide hours of gaming enjoyment at an all new low cost.