You were wandering in a small town, minding your own business, when a young wizard promised you some 24,000 gold pieces to steal a magical orb on his behalf. Naturally, you took him up on his offer of easy gold, only to be (predictably) betrayed when he used the orb to open a portal to the Shadowfell and left you for dead.
Unfortunately for him, you were arrested. Fresh from your jailbreak, assisted by a revenant whose only purpose is to track and kill the wizard who cheated the Raven Queen, you decide: Yeah. You could go for some revenge.