The Twisted Shadow, by Edith Dorian (epub/Kindle/pdf)
Judy Carrington, a college junior, takes a summer job in the library of Sinnett Harbor, a small Maine seacoast town. When Judy meets Assistant Forest Ranger Timothy Wade, she is sure her summer will not be a dull one.
Suddenly, Tim and Judy find themselves entangled in a strange series of events involving a masked intruder who always casts a frightening twisted shadow... Then Judy receives a gasping call for help from the Pulitzer Prize novelist Sandys Winter. When she goes to rescue him, she not only uncovers the masked intruder, but she also finds that even to a forest ranger some things are more important than his work...