The fourth book in the Douglings Adventures series. 

The Douglas family experiences another epic adventure, this time in the ancient Vatican City. There, in the company of St. John Paul II, they explore in, around, and under St. Peter’s Basilica to unearth hidden treasures, surprising discoveries, and a terrifying serpent ready to destroy everything that is holy! With the help of their special saint, a knowledgeable friend, some miraculous objects, and their own quick-witted determination, the siblings work their way through each challenge face an evil that has been festering in the dark recesses of the Vatican Necropolis.