In this documentary, the presenter and art critic Matthew Collings explores how Turner, the artist of light, makes light the vehicle of feeling in his work, and how he found inspiration for that feeling in the waters of the river Thames. JMW Turner is the most famous of English landscape painters. Throughout a lifetime of travel, he returned time and again to paint and draw scenes of the river Thames, the lifeblood of London. This documentary reveals the Thames in all its diverse glory, from its beauty in west London, to its heartland in the City of London and its former docks, out to the vast emptiness and drama of the Thames estuary near Margate. Turner was among the first to pioneer painting directly from nature, turning a boat into a floating studio from which he sketched the Thames. The river and his unique relationship with it had a powerful impact upon his use of materials, as he sought to find an equivalent in paint for the visual surprise and delight he found in the reality of its waters. By pursuing this ever-changing tale of light, Turner also documented and reflected upon key moments in British history in the early 19th century; the Napoleonic wars, social unrest and the onset of the industrial revolution. His paintings of the river Thames communicate the fears and exultations of the time. Turner's greatness as a painter is often attributed to his modern use of colour. Many of his paintings are loved by the British public and regularly celebrated as the nation's greatest art. This film reveals for the first time on television a key inspiration for that modernity and celebrity; a stretch of water of immense importance to the nation in the early 19th century but which today is often taken for granted - the river Thames.