When British Parliament creates an award of twenty thousand pounds sterling to whomever can come up with a solution for determining longitude at sea, a carpenter-turned-clockmaker, John Harrison (Sir Michael Gambon), begins his experiments to build an accurate timepiece unaffected by sea travel. His main obstacles are lack of money, a judgment Board convinced that the answer lies in astronomy and not clocks, and the mechanics of the clock. Rupert Gould (Jeremy Irons), a retired Naval officer who suffered a nervous breakdown in World War I, has been researching Harrison’s history and makes efforts to locate and restore Harrison’s clocks. Harrison’s and Gould’s struggles are linked by the clocks which the two men will, across two hundred years, make tick accurately enough to measure longitude.