"Pop" is an American TV series, the plot of which involves the secret of a music box.

In the play, the music box is an important clue that is used to reveal a complex criminal conspiracy. The music box looks like an ordinary toy on the outside, but there are some secrets hidden inside. When the music box is opened, it plays a specific song, which is actually a hidden code that can be used to reveal the truth.

In addition, the music box has a special mechanism that can trigger an alarm under certain circumstances. This mechanism is used to help the protagonist escape danger at critical moments.

In general, the secret of the music box is a complex puzzle that requires the audience to solve it through the advancement and reasoning of the plot.