In the 18th Century the British Parliament offers a large prize to anyone able to come with an answer to the troubles plaguing sea travel. The problem arises from inability to determine the longitude of travel because of the inability of clocks keeping accurate time at sea. John Harrison (Michael Gambon) is a gifted craftsman who takes up the challenge to create what has today become known as the Marine Chronometer. The challenge is made more difficult for him because of the efforts and bias against him by the Board of Longitude. As this story is told the story of 20th century enthusiast Rupert Gould (Jeremy Irons), who is determined to restore Harrison's original creations, is also told.