A colourfully dressed Bedouin brandishing a sword and wearing an ancient symbol of Christianity interrupts the breakfast of Sherlock Holmes and Dr. Watson with a cryptic message of warning: they must stay away from the affairs of his people.
Before long the world’s most famous detective and his tenacious assistant are dispatched to the Vatican to investigate the murder of Cardinal Tosca. Considered the Pope’s natural successor, Tosca was involved in work of a controversial nature – talk of a lost gospel coincided with the arrival of several mysterious packages from Egypt – and he was killed as he worked on the translation of an ancient scroll. All clues point towards Holmes and Watson’s Bedouin intruder and there are whispers of the involvement of a so-called ‘unholy trinity’.
The duo embark upon a dangerous trip to Egypt, the birthplace of the Coptic Church, to uncover the nature of a parchment missing from Cardinal Tosca’s office and, ultimately, the motives of the Bedouin.