Lark Holds the Key — Natasha Deen

It's the third day of summer vacation, and Lark's halmoni -- that's Korean for grandmother -- has promised to take Lark and her twin brother, Connor, to the library. Only trouble is, they arrive to discover that the town librarian is missing her key to the library. Lucky for her, Lark just happens to be a budding private eye. Can rookie detectives Lark and Connor solve this mystery and recover the lost key?