Mozart String Quartet no. 15 in D minor, K. 421

Wolfgang Amadeus Mozart's String Quartet K. 421/417b is the second of the quartets dedicated to Haydn and the only one of the set in a minor key. Though undated in the autograph, it is believed to have been completed in 1783, while Constanze Mozart was in labour. Constanze stated that the rising string figures in the second movement corresponded to her cries from the other room.