The museum is planning an exhibit of the famous painting "The Old Lady by the Window" and tickets are sold out for the public to see it. The museum's curator receives a note from a man who says he will steal the painting if the museum opens on the day of the exhibition. The curator suggests that the man enter the museum through a one-way door and exit through a locked exit. This way, he says, the thief will not be able to gain entrance to the museum.