Whisper — Barbara Hambly

A novelette of 14,000 words, sequel to Hambly's Darwath series. The teleporter is due to open between the Keep of Dare and an unknown Keep, lost for three thousand years - and Archmage Ingold Inglorion is snowed in fifty miles away and unable to be there to deal with whatever might be on the other side of that teleporter. California warrior-woman Gil Patterson, and California mage-in-training Rudy Solis, have to explore the unknown Keep on their own: to interpret its secrets, to prevent whatever might lurk there from following them back to the last Keep of humankind... and to destroy it when, in spite of their efforts, it does.