The Madonna's Secret.

Drama critic John Earl observes a piece of artwork in a museum, gazing at it reverently. He asks the museum curator how much it costs, and the curator says that it is not for sale. Earl continues his pursuit to find out who the model for the painting was. He learns it is Helen North, a young woman who looks nothing like the woman in the painting. Earl works with the police department to arrange for Helen North to apply for modeling, in order to spy on Corbin.