Hooten is in Rome, and meets with Sister Maria, where she asks him to find one of the legendary Sibylline books of prophecy so important to the Catholic church. Sister Maria is threatened by a member of the Italian Mafia, warning her to not tell Hooten of his plan.
Lady Alex, in Rome looking for a wedding dress withe her mother Lady Lindo, explores the ruins of the city with glee.
Hooten barely escapes thieves on his secret plane ride to Rome, jumping out of the plane, landing in a river.
Hooten meets Lady Lindo in a bar, much to the dismay of Lady Alex. They argue, but Hooten eventually wins her over in his search for the book.
Clues lead them to break into the Sistine Chapel, where they find a chunk of wood hidden inside the ceiling behind the painting of a book.
Analysis of the wood leads them to the basement of a temple nearby, where the book was supposedly kept inside a wooden chest.
They explore catacombs, searching for the chest. They find the chest, matching the wood to the rest of the chest. Opening the chest, they find the book. Before they can leave, they encounter a huge alligator. Hooten brings down the ceiling on top of the alligator, killing it, but it also blocks their way out.
Alex reads from the book, and finds a way out of the catacombs.
Hooten and Alex argue over what to do next. Alex wants to give the book to the Vatican, but Hooten holds firm in his desire to give the book to Sister Maria. It turns out the Italian Mafia is behind this, forcing the Sister to cooperate. The Mafia demands millions from the Vatican in exchange for the book.
Hooten and Alex find a way to escape the mafia with the book, but discover soon after that Lady Lindo has been kidnapped. The mafia demands the book, in exchange for Lady Lindo.
Alex meets the mafia alone, leaving Hooten behind. Hooten eventually catches up, but the mafia intends to kill Lady Lindo, Alex and Hooten as punishment for taking the book. The bad guy shoots Hooten repeatedly, and he falls off the bridge and into the river. The police arrive, and take the mafia boss into custody.
As Lady Lindo and Alex prepare to leave Rome, they find Hooten in the hotel bar, drinking with Sister Maria.
It is there they learn Hooten's first name is Ulysses.