Originally Posted by GeckoFriend
I'm pretty sure it's The Forgotten Door by Alexander Key. He also wrote Escape to Witch Mountain and a couple of sequels. I think all of his books are considered young adult.
Thanks. I was able to find a searchable copy at Amazon and you're right, that is the book. I hadn't realized he'd written the Witch Mountain book or that there were sequels. First time I read any of the book was in Jr. High and I didn't get to finish it then because it belonged to the school and my family moved. Then yrs later I found a copy (currently missing) and read it through. Alas they don't have it for Kindle at the moment.