"The Forbidden Kingdom" is a historical fiction novel that intertwines the stories of two men, a 20th century sailor and 16th century Portuguese poet, Luis Camões. The narrative alternates between the two, exploring the sailor's obsession with the poet's life and the poet's experiences in the East, including his journey to Macao. The book delves into themes of identity, obsession, and the clash of Eastern and Western cultures.

The book revolves around a Swiss classics teacher who, upon encountering a mysterious book by a Portuguese author, becomes obsessed with the life and thoughts of the writer. This obsession leads him to abandon his job and life in Bern, embarking on an impulsive journey to Lisbon. In his quest to understand the author's fate and the resistance movement against the Portuguese dictatorship that the author was involved in, the protagonist explores themes of history, philosophy, and the complexities of human character. As he delves deeper into the past, he encounters various individuals who were connected to the author, piecing together a narrative that challenges his own understanding of life and identity.