Scott, now engaged to girlfriend Izzy, brutally attacked Macs last year and is looking for forgiveness as he revisits Cwmderi.
Harries commented on the upcoming plot: "I think Scott wants to do penance. He says he has been through hell over the past year and wants to be punished for what he did, but on his own terms.
"He thinks that in some confused way if he does his penance then he can carry on with his life and live happily with Izzy.
"I think that he is clutching at straws to think that coming home would give him closure. He's pretty desperate I would say."
Rhys Bidder, who plays Macs, said of his character "For a year, Macs has been trying to get over what happened. But a lot has happened during the year and it's as if Macs has locked the whole thing away in a cage in his mind.
"Seeing Scott again has unlocked the cage and everything has come flooding back. Because of the history between Macs and Izzy, seeing Scott engaged to her has rubbed salt on the wound."
Revealing that Macs is looking for justice, Bidder added: "Macs wants evidence of what happened. But he doesn't want to go to the police because he can't face going through a court case. He wants the power to get what he wants, which is to drive Scott away forever."
Macs and Scott will engage in a violent clash in a dramatic Pobol Y Cwm episode in under a fortnight's time on Tuesday, June 26. Get the Inside Soap magazine on your iPhone or iPad