This first Wells and Wong mystery, Murder Is Bad Manners, is also called Murder Most Unladylike. It's 1933 and Wells and Wong are students at a fancy girls' school in England. Wong is homesick for her house and family in Hong Kong but she has made friends at school, especially with Wells, the daughter of Lord Hastings and a perfect English rose (porcelain complexion, golden hair, etc.) Together they have formed the Wells and Wong Detective Agency and when a teacher disappears suddenly they go to work to solve what they are sure is her murder.
The second book in the series, Poison Is Not Polite, aka Arsenic for Tea, takes place in 1934 at the estate of the Wells family. It's Wells' birthday and in addition to her parents the house party to celebrate includes her brother and his friend from school, two classmates of Wells and Wong, a kleptomaniac great-aunt, a dashing and mysterious uncle, a frumpy governess, and a creepy "art expert" who seems more interested in Wells' mother than the house's art treasures. When he turns up dead, poisoned by arsenic at the children's tea, the girls have the case to themselves while the estate is cut off by heavy rains and flooding.
Also at the house though not really suspected of the crime are the butler and the cook. The book includes a map of the estate and floor plans for the three floors of the manor and a family tree. Perfect.