London, the city where humans and non-humans reside. Mico Serizawa is a girl with the ability to see things that are not human. In place of her late grandfather who possessed the same ability, she travels to London, determined to help others. Starting from Bill, a man who owns a detective agency and was once her grandfather's partner, what changes are there in store for Mico as many other encounters await her? (Source: Kadokawa, translated)

Ningen no Tantei-san is an adaption of Sayuna Sayuki's game of the same title.