Steel Magic
by Andre Norton
A final stand for Avalon...Sara, Greg, and Eric Lowry are exploring the woods near their uncle's Hudson Valley estate when they are magically transported to the land of Avalon. There they meet Huon, Warden of the West. When he tells them that the forces of darkness have stolen the three talismans that protect Avalon-King Arthur's sword, Excalibur; Merlin's ring; and Huon's horn-the children set off on a quest to find the three tokens of power. For Avalon stands as a wall between the Dark and the mortal world. And if Avalon falls, so does Earth....