Book I of The Darwath. Gil Patterson, a graduate student in medieval history, is troubled by realistic dreams with a powerful aura of impending doom and an elderly wizard called Ingold Inglorion. Surely, just a dream...? Days later the same wizard crosses the Void between worlds seeking sanctuary for the last Prince of Dar, and reveals himself to Rudy, a young drifter. But onew of the monstrous, evil Dark ha followed in his wake and in attempting to help Ingold, Gil and Rudy are drawn into the nightmare world of the Dark. And the only way home is to solve the mystery of the Dark... https://cosmiccauldronbooks.com.au/products/the-walls-of-air-barbara-hambly