In a remote part of New Zealand, lies a cold, dark and mysterious cave system with the potential to be the deepest dived cave in the world. It’s here that explorer and hero of the Thai cave rescue Richard “Harry” Harris is searching for a sense of self. There’s no question that this is the highest stakes dive he has ever attempted. Underground, underwater, with a finite amount of gas to breathe, it’s a dangerous game to play. So what drives Harry to continue in his pursuit when he knows the cost - not just to himself, but to those he loves - and will he make it back to them?

• Documentary