High School Detective Agency is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Han Yoojin, a high school student who has everything he needs, is a quiet student at school, but as a CEO who runs a detective agency outside, he solves the problems of the underworld with his friends!