What is an important object in the book The Romeo And Juliet Code by phoebe stone?

In the book "The Romeo and Juliet Code" by Phoebe Stone, an important object is a pendant worn by the main character, Liv. The pendant is made of gold and has the initials "R" and "J" engraved on it. It is given to Liv by her grandmother, who tells her that it was once owned by Shakespeare himself. The pendant is said to have magical powers, and Liv believes that it is the key to unlocking the secrets of the play "Romeo and Juliet".