Out of Time's Abyss is a science fantasy novel by American writer Edgar Rice Burroughs, the third of his Caspak trilogy.

This system forms a thematic element serving to unite the three otherwise rather loosely linked Caspak stories.

They enter the chamber of the Wieroo king, a huge member of the race, and Bradley kills the creature with its own sword.

On the Caspakian mainland, Co-Tan and Bradley begin the trek to Fort Dinosaur, only to find the U33 under the command of its German crew from the first book.

Von Schoenvorts has miscalculated the resources necessary for their journey home, forcing the German crew to sail back to Caprona to replenish, and in the process capturing the rest of Bradley's men.

Together, the survivors search for Bowen Tyler and Lys La Rue, who were lost in the jungles in the first book.

Once the Uboat escaped via the cave river, the survivors meet the party from the outside world from the previous book, and they return home to America, where Bradley will marry Co-Tan.