Key Out of Time: Time Traders, Book 4 (Unabridged‪)‬

It's a good thing that Time Agents are intensively trained. When Ross Murdock and Gordon Ashe set up a time gate on the alien world of Hawaika for an exploration into its troubling past, they didn't anticipate that a storm would sweep them and their helper Karara Trehern and her two dolphins through it unprepared...and then collapse the gate.

Trapped in a time of sword-and-spear technology, they rapidly discover that each of the world's cultures appear to be trying to wipe one another out. But then Chance reveals that this is being manipulated by the spacing civilization, the Baldies, that created the disk-map that enabled them to find Hawaika. And their best shot at surviving will be to pit the magic of the Foanna against the advanced technology of the Baldies. But the Baldies are moving even now to exterminate the Foanna!