Joel Rosenberg - [Keepers Of The Hidden Ways 03] The Crimson Sky

In earlier books, three young college friends discovered timeless, secret portals into the alternate world called Tir Na Nog and successfully located two magical jewels. Now they seek a third jewel as struggles between noble ruling houses push them perilously close to war. Meanwhile, at home in the "real world, " an evil being is stalking family and friends of one of the young heroes. Now they must find the stone, defuse the increasingly volatile political situation n Tir Na Nog, and stop the evil one before he can destroy more innocent lives