1: a thief is caught redhanded by his would-be target and isn't handed over to the authorities.. on a few conditions. This can be modern, or supernatural based.
2: a shapeshifter belonging to a royal bloodline is traded off to curb war, or is kidnapped to initiate war, and his captor finds a new use for the prince.
3: a werecreature vagrant is taken in by a higher classed individual. In exchange for protection and a home, certain services are required from the werecreature.