Bonita Granville has the title role in "Nancy Drew and the Hidden Staircase," the final entry into the Nancy Drew series. It also stars Frankie Thomas and John Litel. This particular film is based on one of the actual books, but how closely it sticks to the story - well, I haven't read Nancy Drew in nearly 50 years, so I can't remember. Since in the books, Nancy had two girlfriends, missing in the series, it probably doesn't stick all that closely.
In this one, Nancy is determined to make sure that two elderly sisters keep to their father's will so that the house can be donated to a hospital. That won't happen unless at least one of them is in the house every night for twenty years. With only two weeks to go, and their chauffeur shot dead in the house, the ladies want out - fast.
Nancy manages to drag Ted Nickerson, her quasi-boyfriend, into all kinds of trouble, and that's where the fun happens. Thomas is a riot. Nancy always got into deep water in the books, but I remember her as more serious and perfect. That wouldn't have worked for the films, so Nancy is kind of a Lucy and Ted is Ethel, an unwilling participant in her schemes.
Bonita Granville was a fine movie Nancy, very lively, wacky, and likable. It's a shame there are only four "Nancy Drew" films. It is a very good series.