Amos didn't believe at first, but when Jesus rose from the dead and Amos witnessed His ascension, Amos knew he had been completely wrong. Jesus is alive and who He said He is! Now Amos is among the many Believers who must be careful because of persecution. Amos is a friend of Saul of Tarsus who is obsessed with destroying any and all Christians he can find. Amos wants to lead his friend to the Lord, but it is so dangerous to reveal his belief to Saul. When Amos is assigned the task of figuring out a signal for Christians to safely identify other Believers, he learns that he is being sought - by Saul, who doesn't know the one he is trying to find is his friend.
This is such a good fictional story based in fact, for middle grade and up.

https://www.goodreads.com/book/show/61898534-amon-s-secret?ac=1&from_search=true&qid=y2fTw96pTf&rank=2