Our story starts off where the Gospel of Luke left off—Jesus is back.
Now that he's resurrected, Jesus decides to hang out and chat with his disciples (whom Luke calls apostles) for forty days. The fun can't last forever, though, and Jesus ascends into Heaven on a cloud. What can we say? The guy knows how to make an exit.
What are the apostles supposed to do now? Luckily, Jesus left very specific instructions. First, they're to spread his message to the ends of the Earth. Second, they're supposed to pick up his dry cleaning. Jesus loves freshly laundered robes. Ok—not so much on that whole second part. Plus, the first part should keep them plenty busy.
So the apostles get to work. Peter takes the lead and they all preach and teach about how Jesus is the Jewish Messiah and the fulfillment of everything that Jewish scripture says will happen. Awesome, right? They also perform lots of miracles (your run-of-the-mill healing and raising from the dead… no biggie). Oh, and their preaching also makes the religious authorities in Judea very, very mad. Like master, like disciples. The whole crew gets arrested a couple times (luckily, angels break them out of prison—angels are crafty like that) and one of the disciples, Stephen, even gets stoned to death. It's a bad time to be a believer.
But because God likes irony, one of the guys involved in the death of Stephen gets converted (and blinded) when he's on his way to Damascus to persecute some more Christians. He changes his name to Paul and takes up the discipleship torch. Paul and some friends travel all around the Roman Empire talking about Jesus non-stop. He has all kinds of zany adventures. He's stoned, worshiped as a god, starts riots, and talks so long that people fall asleep. He's also pretty good at the whole spreading-the-word-of-God thing and he manages to set up churches in loads of different cities around the Empire. Go, Paul.
Meanwhile, back in Judea, there are issues. When Peter sees a vision from God, he realizes that Christians have got to branch out and start trying to convert Gentiles (i.e., non-Jews) as well as Jews. This is big. Like Mark Zuckerberg creating Facebook big. Paul thinks this is a swell idea, but he just wants to know one thing—do Gentile converts need to follow Jewish law and be circumcised? Because that's gonna make convincing the guys to join up a little bit harder.
Finally, Paul manages to tick off enough people and he's arrested when he comes back to Jerusalem to visit. This time, it's the Jewish people who are against him (they're mad about the whole you-don't-have-to-follow-Jewish-law-if-you're-Christian thing). The naysayers haul him before Roman authorities and Paul is tried and held as a prisoner for a really long time. We're talking years.
Finally, he gets tired of all the nonsense in Judea and asks to be shipped to Rome so he can take all this up with the emperor. Paul lands on Roman soil and is welcomed by the church there. He hangs out for a couple years, but we never find out what really happens. We've got a hunch it's not good, though. Poor Paul.