"Behind the Green Door" is a psychological thriller novel by author Mildred A. Wirt. The story revolves around a young woman named Penny Parker who is an amateur detective and a journalism student. Penny is an intelligent and curious young woman who has a passion for solving mysteries. In the book, Penny receives a mysterious invitation to a mansion where she is tasked with solving a puzzling mystery. The mansion is owned by the wealthy and reclusive Mrs. Weems, who has a dark secret behind the green door in her mansion. As Penny investigates the mystery, she is faced with danger and intrigue, as she discovers the truth behind the green door.
The book is filled with several other intriguing characters, including Penny's friend and fellow journalism student Louise Sidell, who assists Penny in her investigation. There is also the mysterious and sinister caretaker of the mansion, Joe Quigley, who seems to be hiding something. The book also features Mrs. Weems' troubled and traumatized daughter, Janice, who is a key player in the mystery behind the green door. Overall, the book is a thrilling and suspenseful mystery with an array of interesting and complex characters.