The Penny Parker Mystery Stories were published from 1939-1947 and written by Mildred Wirt, who of course also ghosted many of the early Nancy Drew books. There were many similarities between Penny and Nancy. Both were being raised by widowed fathers and both had a motherly housekeeper. Penny is sixteen and lives in the Midwest. She has her own car, and like Nancy, loves a good mystery. Many believe that Penny is the Nancy Drew Mildred envisioned. Her stories are more time specific; Penny refers to the "enemy", and there are references to other wartime situations as well.
Published by Cupples and Leon, Mildred seems to have more control over the development of the series than Stratemeyer's Nancy Drew. Penny certainly gave Nancy a run for her money, and seventeen volumes were published. The earlier, thicker volumes one finds in this series seem sturdier, while later volumes, printed during the war do not seem as substantial. I was fortunate to find several of these at a local used bookstore, and bought them all without knowing a lot about the series. It was one of my more fortuitous purchases, as I have never seen several all available in a store again.
Beyond the Green Door is set in a ski resort area in the middle of the winter months. There is a hotel with strange happenings going on behind a green door. Penny attempts to help a struggling lodge owner, and uncovers dangerous situations. The book is a fast read, and perfect for a cold, snowy Saturday afternoon.
I highly recommend these books. Like most series book fans, Millie Benson is one of my favorites, and I never seem to be disappointed when I read one of her books.