The Fireball Trilogy Series by John Christopher

Two cousins are thrust into a parallel reality when they travel through time and fire in the first book of the alternative history Fireball Trilogy, from critically acclaimed Tripods author John Christopher. Simon and his cousin Brad hadn t wanted to spend the summer together. And the quiet London suburb where Simon lived was the last place they expected anything unusual to happen. Then the fireball came... moreTwo cousins are thrust into a parallel reality when they travel through time and fire in the first book of the alternative history Fireball Trilogy, from critically acclaimed Tripods author John Christopher. Simon and his cousin Brad hadn t wanted to spend the summer together. And the quiet London suburb where Simon lived was the last place they expected anything unusual to happen. Then the fireball came. The huge whirling ball of light was like nothing the boys had ever seen before and they felt compelled to investigate. They awoke in a world where everything had changed. It's still England...but an England terrifyingly different from the one they had left behind. They passed through the fireball, and now they will have to learn to survive in the fascinatingly strange world on the other side " less

Encountering a fireball which turns out to be a crossing point between their world and another one on a different probability track, two boys, one English and one American, face Indians, Vikings and Aztecs in their attempts to reach California. Sequel of Fireball.

Simon and Brad's fireball adventures take them to ancient China where they are exposed to incredible practices of mind control.