The Trumpeter of Krakow question

Q.1-Summary.
Set in 15th century Poland, This book is the story of a young boy’s admiration for the bravery of a long-dead youth and how this encourages him to remain loyal to his country as a trumpeter, in the face of great danger.
Forced to abandon their farm and house to the invading Tartars, Joseph Charnetski and his parents flee to Krakow with the only thing that they managed to salvage —a priceless family gem called the “Great Tarnov Crystal” (placed in a pumpkin for protection). Believed to have strange magical powers that will guarantee victory to anyone who possesses it, therefore, everyone wants to get it. The Crystal must be delivered to the king before it falls into the wrong hands (Peter of the Button Face most likely).
When they got there, they find themselves homeless and knowing no one the see. But that didn’t last for long: Joseph found and rescued a girl and a alchemist, who offered them a place to stay. At this offer, they accepted. With Joseph’s father now the replaced trumpeter of the city, Joseph was determined to follow and remember the notes that his father played. One night, when all were asleep except Joseph, his father, and the evil mind of Peter of the Button face, Peter attacked the tower of the trumpeter. Quickly remembering the secret that he made with Elzbietka in time of danger, Joseph played an extra 3 notes at the end of the song. Elzbietka Quickly notified Jan Kanty, the well-known scholar of the city. Worried, Jan Kanty sent some guards to save them. The guards were successful. The king came back just two days earlier. When the king came back, Joseph’s father handed the king the prized jewel. But this did not last for Pan Kruez (the scholar) had grabbed the jewel and fled towards the river. Once he got there, he threw the jewel into the water, and the on-going quest for the most-wanted jewel had finally ended.