Out of Time's Abyss is a direct sequel to The Land That Time Forgot and The People That Time Forgot, continuing the lost world saga begun in the earlier stories. It connects the previous two installments, bringing in characters introduced in each. Burroughs completes the revelation of his lost world's unique biological system, only hinted at in the previous installment, in which the slow progress of evolution in the world outside is recapitulated as a matter of individual metamorphosis. This system forms a thematic element serving to unite the three otherwise rather loosely linked Caspak stories.The book begins with Bradley, who had left Fort Dinosaur on an expedition in the first novel and never returned. Bradley and his party are attempting to return to Fort Dinosaur. Along the way, they encounter a creature which appears to be a flying dead man. Some of the members of the party consider it to be a ghost or banshee. Tippet is convinced that he is soon to die, and the next day he is