David Jason is the only survivor on a submarine that was sunk during the second world war, although he can not remember what happened. In 1981 when the apparently same submarine, is discovered in perfect working order, it is decided to hold an investigation using a modern day crew, by taking it back out and retracing its last known route. David Jason and the submarine's builder are invited along in an advisory capacity.
Events during the journey, resemble the unfortunate mishaps of the previous voyage, and even some of the crew start behaving in a similar reckless manner to their predecessors. Are the events in the ship just illusions? and is it 1943 again or still 1981? who is it that they are about to engage with?
David Jason must quickly sought out what is reality and what is not, as his memory concerning the previous trip begins to the return. If his theory is correct, can he stop an even much bigger disaster than originally happened in 1943, and at what price??
David Jason, as always, in marvelous in this. Great entertainment and a very fine film.