The film is about Beijing-based author and scuba instructor Steven Schwankert's search for the British submarine HMS Poseidon.

He spent the next six years working on the project, bringing together research in China and the UK to piece together the history of the submarine.

The film charts Schwankert's efforts to examine the escape and the accident in unprecedented depth.

The story is also told in Schwankert's book Poseidon: China's Secret Salvage of Britain's Lost Submarine.

Further scenes were shot in the UK, specifically at Gosport's Royal Navy Submarine Museum, at the Dock Museum in Barrow-in-Furness, at the National Archives in Kew, London, and in and around south London, where the grave of Poseidon escapee Patrick Willis was assumed to be located.