Magic exists in the world, but it is kept hidden so that the normal people do not lose their minds and go on a crusade against people who are different. In order to keep magic from being let loose on the world there is a secret council that makes the laws and uses their own police force to ensure these laws are followed. If you have more questions feel free to send them to me and I will do my best to answer them.
The idea I have is a person with magic likes to push the limits of the law, they like to do street magic to win bets and money from normal people. They also have been rumored to use their magic to sneak into places and steal things every now and again. Yet they have not committed any crime that would warrant arrest and punishment. But after a while, they are caught up in something, something that forces them to team up with the police.
The other character would be someone who works for this magic police force. Unlike the normal police this group does not wear uniforms or work shifts, they are always on duty and regardless of what they are doing, they are forced to respond when summoned by the council. They are known within the group as working alone, their luck is not the best when it comes to having a partner. So in their wisdome the council assigns thei loner as new partner, the criminal.