Out of the silent movie era and the heady heights of 1920s Hollywood, Mack and Mabel tells the heart-wrenching love story of two of its greatest legends, Mack Sennett, The King of Comedy, and his comedienne star Mabel Normand. The action takes place in flashback, as Mack, wandering uselessly around the set of a new 'talkie', reminisces about his glory days of Keystone Kops, custard pies and bathing beauties, in the days when movies were movies and sound came from a piano.