damn... i would love 2 play the Thief...
anyways let me get this straight: you got the main character (with hidden talents) who is just a a regular "player" in society, all of a sudden a crime is committed against "society" (guessing is the kingdom, maybe a stolen relic, or kidnapped the prince) the thief is chased, but he hides the item... as the investigation goes, Daiske (main character) awakens some form of power and is found guilty of the crime because the power has a direct link to the "artifact" or Crime committed... little does he knows that the item/Prince is then left somewhere out of Daiske's reach UPON capture. (arrangement's to meet, not found, etc, or lends "it" to some friend and artifact isn't return for ">.> I got capture" purposes)
Presented in front of the Queen after capture, with witnesses of his power (or he+prince in same place) he is sentence to death. he then is trow into a form of transportation. (train?)
Fallow by this, u get 2 wardens (that are a couple) keeping an eye on the prisoner, but because they are too lovely-dobly (or they get into an argument) don't get their job right and are caught off guard by some Mysterious figure (usually an enemy country's army, or a road gang looking for money) and is led free as an exchange of lending them his powers (or something along those lines)
hmn... nice story... now, how do you get Hades, god of the Death and Jewelry interested into all this? ... is the artifact his? or he wanted the prince death?
Also this is all just off the top of my head, plz do let me know if I got it completely wrong =D trying 2 figure out how u'll pull it off in S4