As the followers were scattered about the Eastern Mediterranean area, churches were established in various places. News of the church in Antioch reached the church in Jerusalem, and Barnabas was sent to the Antioch where many Greek people were to the Lord. Barnabas travelled to Tarsus and brought Paul to Antioch where they worked together.
Another follower from Jerusalem arrived in Antioch and predicted a severe famine over the entire area. The followers in Antioch decided to send help for the followers in Jerusalem. Their gift was carried by said Paul and Barnabas. (Note: the disciples were called Christians first in Antioch.)
In Jerusalem, Herod and some Christians arrestedin one line we are told that James, brother of John, is executed by the sword.
Peter is among those arrested. While sleeping in the prison, Peter is rescued by an angel. Finding himself safely outside, he goes to the home of Mary mother of Mark where many people gathered and were praying for him. A servant named Rhoda answered the door and recognized him. She is not believed. When Peter keeps knocking the others open the door and are astonished.
Note: one line about James being killed and the rest of this chapter devoted to Peter.
Note also: Peter tells the others to "tell James and the other brothers and sisters about this (his escape)." Since James apostle has been killed, I presume this James would be Jesus brother James, who has joined the apostles in Jerusalem.
Chapter 12 ends abruptly, switching from Peter to say: when Barnabas and Saul and finish the mission, they returned from Jerusalem, taking with John, also called Mark.