Mildred A. Wirt Benson was an American journalist and author, born in 1905 in Ladora, Iowa. She is best known for her work as a ghostwriter for the Nancy Drew series of children's books under the pen name Carolyn Keene. Benson wrote the first 23 Nancy Drew books and continued to contribute to the series throughout her life.

However, one of Benson's lesser-known works is the novel "Behind the Green Door," which she wrote in 1933 under the pseudonym Ann Wirt. The novel is a mystery and adventure story set in the Midwest during the 1930s, and it features a young woman named Carol who finds herself caught up in a dangerous criminal conspiracy.

The story begins when Carol, a recent college graduate, takes a job as a secretary for a wealthy businessman named Edward Norton. Norton seems like a charming and respectable man, but as Carol becomes more involved in his business affairs, she realizes that he is involved in some shady dealings. Norton is involved in smuggling and counterfeiting, and Carol is soon drawn into a dangerous web of intrigue.

As Carol tries to unravel the mystery behind Norton's business dealings, she faces a number of obstacles and dangers. She is followed by shadowy figures, threatened with violence, and even kidnapped. But with the help of her friend Ted, a reporter for a local newspaper, Carol is able to uncover the truth about Norton's criminal activities and bring him to justice.

"Behind the Green Door" is a gripping and fast-paced novel that showcases Benson's skill as a storyteller. Like the Nancy Drew books, it features a plucky and resourceful heroine who faces danger with courage and determination. But "Behind the Green Door" is also a more mature and complex work than the Nancy Drew series, with a darker and more realistic tone. It deals with issues like corruption, violence, and greed, and it portrays a world that is more morally ambiguous than the one in which Nancy Drew operates.