a score to settle
An old problem, grudge, or grievance (with or against someone or something) that one wishes or intends to redress or rectify. I've had a score to settle with my brother ever since he ran away with my wife. The former champion entered the competition with a score to settle, after being knocked out of the tournament last year by a newcomer. There are a few scores I still need to settle with my old bosses, but otherwise, I've pretty well moved on.