Byun Bakehyun is the best jewel thief anyone can hire. Aslong as you have the money to pay for it, he can get you even the most valuable piece of jewel in the whole world. 

Mr. Park Jungsoo hires him to get the most valuable Blue Diamond and Baekhyun meets someone that captures his eye on the way. The CEO fails to give Baekhyun his payment and as a result, he takes his son, Park Kyungsoo.