In the vaults of the Vatican City, buried between obscure codices in her office in the Secret Archive, Sister Ottavia Salina, a paleographer of international prestige, receives a commission to decipher the strange tattoos found on the body of a dead Ethiopian: seven Greek letters and seven crosses. Next to the body, three apparently worthless pieces of wood were discovered. Scholars suspect that these pieces of wood may be from the Vera Cruz -the true cross of Christ-. Accompanied by Professor Boswell, an archaeologist from Alexandria, and by the Captain of the Swiss Guards of the Vatican, Kaspar Glauser-Ro'st, the protagonist begins an investigation to uncover the mysterious forces behind the disappearances of holy objects from churches around the world and sets of on an enigmatic adventure to uncover seven answers based on the seven capital sins, in which Dante and his vision of Purgatory in the Divine Comedy seems to have the key. The search for these answers takes them to seven cities -from Rome to Antioch, passing through Ravenna, Athens, Jerusalem, Constantinople and Alexandria- on a risky and electrifying journey to discover the identity of the last Cato.