During the darkest days of World War II, the Japanese cargo ship Lisbon Maru sails through the East China Sea carrying hundreds of British prisoners of war. Unaware of the prisoners on board, an American submarine torpedoes the vessel, setting off a desperate fight for survival. As the ship begins to sink, Japanese forces lock the British POWs inside the cargo holds, leaving them to die. In the chaos, some manage to break free, while hundreds are lost to the sea.

Eighty years later, independent Chinese marine physicist Fang Li sets out to uncover the truth behind this forgotten tragedy. After discovering the underwater wreckage of the Lisbon Maru, Fang and his team launch a global investigation, tracing survivors, descendants, rescuers, and historical records across continents.

Through powerful testimonies, archival research, international inquiry, and finely crafted animation, the documentary brings a buried chapter of history back to life. It reveals the terror and courage of the British POWs, the selfless heroism of the Zhoushan fishermen who risked everything to save them, and the complex moral landscape of war.

Lisbon Maru is more than the retelling of a wartime disaster. It is a moving meditation on memory, humanity, and the enduring power of compassion in the face of cruelty.