The Defiant Agents: Andre Norton

Book III of Time Traders. Travis Fox, once the unwilling captive of the runaway spaceship Galactic Derelict, has volunteered - eagerly this time - for the mission to colonise Topaz. But when he and his fellow Apaches find themselves reverting to the ways of their ancient warrior-race, just as the expedition from Russia has been transformed into a Mongol horde encamped across the mountains, it becomes clear that more than their own lives are at stake... Cover art by Davis Meltzer.