In the Boston library, a scream was heard—later leading to the discovery of a body. Four strangers who happened to be in the same place at the same time become close friends, not realizing that one of them knows what happened in the library. Hanna, a well-known writer, is working on a book, not knowing the city of Boston very well, but she’s helped by a caring pen-pal friend who is ready to provide materials for the manuscript.