Rolling mists obscure the time traveling of Claudia and Evan as they leave siblings on a Maine island for the Iron Age of Ireland -- via an old hermit's muddled directives about the ""Other Place,"" a crow who responds only to cuss words, and an ancient bronze figure. The children find themselves in the thick of mythic battles fought by magic, outsize humans of lopsided magnificence -- or just plain nastiness. Fergus, also a time traveler in a sense as he is reputed to have returned as a ghost to dictate to 7th century scribes, dominates the scenes of terror, death, doomed journeys and clandestine plots -- for it was Fergus who held in trust the powerful sword belonging to his foster son Cuchulain, the Hound of Ulster, which would lead the hero to the Otherworld at his death. The children adjust as well as they can to talismans electric with taboo and to the capricious, snarling, gloomy and wise-cracking people they find so frequently bewildering. Claudia, fascinated by and devoted to sad Fergus, acts as his emissary among exiled Ulidians and rallies them with an enchanted bead. Then Claudia, horrified to discover that she is considered immortal, even by Fergus, and therefore expected to undergo a sacrificial death, barely escapes with Evan to Maine. The characters are stirring creations, from a ferocious Queen Medb to a kitchen matron called the ""great Mother,"" and although the plot is labyrinthian it's well worth staying on for the surprises and layered revelations at every turn.