John Comyn was a man in Scotland in the 1300s who was rivals with Robert the Bruce. They both wanted to become the king of Scotland. Robert the Bruce wanted to get rid of his rival so he could then become the king. They wanted to both be loyal to Scotland so they didn't want to do anything bad. But one day in a church, Robert the Bruce snuck up on John Comyn and then fought until Robert the Bruce finally won when he killed John. Robert became the king, but he didn't tell anyone  so he loyalty would go away.