In the far future, the Heliothane Dominion is triumphant in the solar system, after a bitter war with their Umbrathane progenitors. But some of the Umbrathane have escaped into the distant past, where they can position themselves to wreak havoc across time and undo their defeat. The most fanatical of them is the superhuman Cowl, more monstrous than any of the creatures outside his prehistoric redoubt.

Cowl sends his terrifying hyperdimensional pet, the torbeast, hunting through all the timelines for human specimens. It sheds its scales -- each one an organic time machine -- where...