"Adventure in Notre Dame. The Treasure of a Restorer. Part 1"

One beautiful sunny day, a young Canadian turns up at the shop of Archont Duval. The stranger wishes to solve the mystery of his great grandfather's letters. All clues lead to Notre Dame. Archont and his young relatives accompany the stranger to Paris to find the hidden treasure. Will they be able to untangle the messages coded in the great grandfather's letter from his oldest and dearest friend?