Looking for a story

Hello,

I am looking for a story i read some time ago. The plot was a boy pulled from earth and placed onto the body of a girl in a medieval time. She used her knoledge of our technology to i.prove lice and to eventually build up to face zome unknown enemy in the far distant future.

I would love help reconnecting to this story again. I loved it.

Also. Any other realky great storie links are always greatly appreciated.

Wyld