From Aarinfantasy:

The young Yamato Yousuke searches for a way to follow in the steps of his father, a detective who passed away in mission trying to save a little kid who got kidnapped. Finally, an opportunity to become a detective himself has arisen, but in the middle of carrying out his first assignment, a test to see if he would be a good detective, Yousuke suddenly gets hired, apparently for no reason. There must be a secret behind all this...