The Wandering Fire

The Wandering Fire is the second novel of Guy Gavriel Kay's critically acclaimed fantasy trilogy, The Fionavar Tapestry. A mage's power has brought five university students from our world into a realm where an ancient evil has freed itself from captivity to wreak revenge on its enemies.
The ice of eternal winter has reached out to enshroud Fionavar, the first of all worlds. For the Unraveller has broken free after millennia enchained and now his terrible vengeance has begun to take its toll on mortals and immortals, mages and warriors, dwarves and the "lios alfar", the Children of Light. Only five men and women of our own world, brought by magic across the Tapestry of worlds to the very heart of the Weaver's pattern, can hope to wake the allies they so desperately need.
Yet none can foretell whether even these beings out of legend have the power to shatter the Unraveller's icy grip of death upon the land.