Castaways in Time — Robert Adams

A WHIRLWIND IN TIME It was a storm to end all storms, and when it was over Sebastian Foster and his five unexpected house guests--all refugees from the fury of the wind and rain--should have been happy just to be alive. But when the clouds finally cleared, the world outside Bass's home was no longer the twentieth-century America they all knew. Instead, through some bizarre twist in time, the six of them had ended up in England's past. But it was a past that never existed in any history book, a place where the Church was waging a holy war to depose Arthur III and make his nephew king of England and Wales. Thrust into this barbaric world of bloody combat, the time travelers were quick to realize that their modern weapons and knowledge could change the whole course of this England's future--and maybe help them find their way home again--if the warring factions didn't destroy them before they even had a chance to get started...