"The Witness" is a novel that explores the life of a young European boy who is the only survivor of a shipwreck in the 16th century. He is found and raised by a tribe of Indians in South America, where he spends ten years of his life. The boy is eventually found by a band of Spanish conquistadors and returns to Europe, where he becomes a well-respected scholar. The story unfolds as the man, now in his 90s, recounts his experiences and struggles to reconcile his European identity with his decade-long immersion in the tribal culture.

The novel follows the story of a young man who becomes fascinated by his reclusive and eccentric Uncle Petros. As he delves into his uncle's past, he uncovers Petros' obsession with proving Goldbach's Conjecture, a famous unsolved problem in number theory. This obsession led to Petros' alienation from society and ultimately his downfall. The book explores themes of mathematical obsession, family relationships, and the fine line between genius and madness.