There's Something Wrong with the Chief: Du Zhu You Bing (Novel) Vol. 3 Novel

Xiahou Lian, the Qielan Clan’s youngest assassin, needs to get inside the aristocratic Xie household for his next assignment. He secures a post under Xie Jinglan, the family's youngest son, and all players are in position. Yet as the date of the planned assassination approaches, the two boys find that they've become fast friends. Thus, Xiahou Lian takes a course of action that will haunt him for years to come… As fates turn, Xiahou Lian is reduced to working as a dog for the chief of the Eastern Depot, a Ming dynasty spy agency. But the chief is the very boy Xiahou Lian once saved! What’s more, he seems more charming than resentful. There’s definitely something wrong with the chief…