«Murders for Sale» by Andre Norton, Grace Allen Hogarth

When Fredericka Wing arrives in a tiny New England town, it seems an ideal place for a working summer vacation. She plans on managing Miss Hartwell's bookstore while writing. She never dreamed she would find a body in a hammock in her own backyard.

Someone brutally murdered Catherine Clay, an heir to the Sutton family fortune. And more violence follows.

Together with Peter Mohun, a professor at a local college, Fredericka sets out to discover the murderer's identity…and unravel the secrets of the wealthy and powerful Sutton family!

Also published under the title Murders for Sale.