The 1947 film "Secret Beyond the Door" is a mystery film about a young American woman, Celia Barrett (Joan Bennett), who visits Mexico and meets a mysterious man, Mark Lamphere (Michael Redgrave), from Virginia. They fall in love quickly and are married. Mark begins acting strangely, leaves for New York, and tells his wife to go to the family estate in Virginia. When the wife arrives at the estate she finds out that her husband was married before and has a son and an unmarried older sister living with him along with a few servants. When Celia and Mark meet In Mexico they visit a wishing well which has many coins under the water. Mark suggests throwing centavos in and Celia throws one in. At the Virginia house Celia sees some of Mark's pocket things on a table including some coins and a key.

Celia Barrett is a wealthy young New York woman who has had many lovers but doesn't want to be tied down by marriage. She is invited by two friends to join them on a vacation in Mexico.

At the small Mexican town where she is staying she witnesses a knife fight between two men and sees an older American man watching her. He comes over her and introduces himself as Mark Lamphere, an architect visiting from Virginia. They spend all of their time together and at one point visit a wishing well.

Mark makes a comment about a man getting rich by sweeping up the centavos in the well. Celia then throws a coin into the well.

The coin makes some ripples in the water. Mark and Celia then get married at a local church.

They move to a rustic hotel for the honeymoon but Mark uses excuses to put off the usual activity.

Mark owns and publishes a small architecture magazine and he tells Celia that he has to go to New York to sell the magazine. He asks Celia to go to his Virginia estate. Celia takes a variety of trains to Virginia and arrives at the estate where she meets Caroline Lamphere (Anne Revere), Mark's older sister, and Miss Robey (Barbara O'Neil), a rather odd servant.

Celia learns that Mark was married before, that his first wife died, and that he has a son, David. She also learns that Mark is broke and that the estate is mortgaged.

David is a somewhat stuffy boy who tells Celia that Mark killed his mother. Mark and Celia finally get together and then throw a housewarming party for the neighbors. Mark shows his guests six rooms which he has designed to resemble rooms where infamous murders occured. There is a seventh room which Mark refuses to show his guests. Caroline tells Celia about Mark's (and her) mother and Mark's first wife who died of some illness. Some people remark that Mark had married a wealthy woman and when she died he married another wealthy woman. Celia becomes increaslingly worried about her marriage and leaves twice but returns. While Mark takes a shower Celia spots some of his pocket items on a table.

The coins appear to be then current US silver coins including a Walking Liberty half dollar and a Washington quarter. Celia is more interested in the key which is to the mysterious room number seven. She makes a wax impression of the key and after having a new key made she enters the room.

She sees something horrifying and leaves.

Celia and Mark have a discussion and Mark complains that he has always been dominated by women, first by his mother, then by his sister, and then by his first wife. Mark tells Celia that he is going to free himself. He sends David to a private boys school and his sister decides to leave. Mark then fires Miss Robey.

Celia decides to sort things out with Mark and waits in room number seven.

Mark arrives holding a scarf in a menacing position and reveals that his mother had affairs with men and that he had mixed feelings about her.

Celia stands her ground and then they both smell and notice smoke as the house is on fire.

Mark rescues Celia which ends her thoughts about Mark wanting to kill her. It is implied that Miss Robey set the fire.

Joan Bennett as Celia Barrett
Michael Redgrave as Mark Lamphere
Anne Revere as Caroline Lamphere
Barbara O'Neil as Miss Robey
Director: Fritz Lang
Writers: Silvia Richards, Rufus King