Matthew Collings explores how Turner makes light the vehicle of feeling in his work, and how he found inspiration for that feeling in the waters of the River Thames. Throughout a lifetime of travel, he returned time and again to paint and draw scenes of the Thames, the lifeblood of London. The film 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 its estuary near Margate. Turner's greatness as a painter is often attributed to his modern use of colour and many of his paintings are regularly celebrated as the nation's greatest art. The 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.