John is searching for that moral compass that he lost at the end of season 4. He discovers that Chechnya is the wrong place for him to discover his moral compass. Things do not go according to plan for him, and there’s something that happens in the first three episodes that is fairly significant and it’s the circumstances that will ultimately bring him back to Star City, but he’s not going to be the same. He’s not going to be able to live his life the way he had been living it before
Marc Guggenheim about John Diggle in Season 4 (x)
Bonus: This all leads to a very Dig and Oliver-centric episode in the fourth outing.