Nancy Drew and the Hidden Staircase is a 1939 American mystery film directed by William Clemens and written by Kenneth Garnet. It is fourth and last in a series of films starring Bonita Granville as teenage amateur detective Nancy Drew, Frankie Thomas as her boyfriend, and John Litel as her father. It was loosely based on the novel of the same name by Mildred Wirt Benson. The film was released by Warner Bros. on September 9, 1939.

Plot
The elderly Turnbull sisters want to donate their mansion for a children’s hospital. However, their father’s will states that at least one of them has to stay in the house every night for twenty years before they can inherit the estate; there are two weeks left to go.

Then some strange things start occurring. A stranger forces his way past Nancy Drew (Bonita Granville) and brazenly searches the Drew house for related affidavits her lawyer father Carson (John Litel) has obtained. Then, the Turnbulls’ chauffeur Phillips (Don Rowan) dies, though it is uncertain if it was a murder or a suicide. The frightened old ladies consider leaving their home. When Nancy recognizes the dead man as the trespasser, she begins investigating, dragging her boyfriend Ted Nickerson (Frankie Thomas) into one predicament after another, eventually getting him fired and jailed.

When police Captain Tweedy (Frank Orth) arrests the two sisters for Phillips’ murder, their ownership is endangered. Just in time, Nancy and Ted discover a secret passageway in the basement linking it to the neighboring house, owned by Daniel Talbert (William Gould). Talbert would make a lot of money if a racetrack were to be built on the two properties, but the Turnbulls had turned down an offer to buy their place.

Cast
Bonita Granville as Nancy Drew
Frankie Thomas as Ted Nickerson
John Litel as Carson Drew
Frank Orth as Captain Tweedy
Renie Riano as Effie Schneider
Vera Lewis as Rosemary Turnbull
Louise Carter as Floretta Turnbull
William Gould as Daniel Talbert
George Guhl as Smitty
John Ridgely as Reporter
William Hopper as Reporter
Creighton Hale as Reporter
Frank Mayo as Tribune Photographer
Frederic Tozere as District Attorney’s Investigator
Don Rowan as Phillips the Chauffeur
Dick Elliott as McKeever
Jack Mower as Ice Company Dispatcher (uncredited)
Cliff Saum as Burt the Iceman (uncredited)