what is the play about?
Its a story about a show boat called the "Cotton Blossom".
Show Boat
the show boat "Cotton Blossom" arrives at the river dock in Natchez, Mississippi. The Reconstruction era had ended a decade earlier, and white-dominated Southern legislatures have imposed racial segregation and Jim Crow rules. The boat's owner, Cap'n Andy Hawks, introduces his actors to the crowd on the levee. A fistfight breaks out between Steve Baker, the leading man of the troupe, and Pete, a rough engineer who had been making passes at Steve's wife, the leading lady Julie La Verne. Steve knocks Pete down, and Pete swears revenge, suggesting he knows a dark secret about Julie. Cap'n Andy pretends to the shocked crowd that the fight was a preview of one of the melodramas to be performed. The troupe exits with the showboat band, and the crowd follows.

which stage musical was groundbreaking when they used ballet to further the plot of the story UNANSWERABLE by whom was this musical directed? Francesca Zambello.
wiki:1855242
Show Boat [SEP] Synopsis
Note: Although the basic plot of "Show Boat" has always remained the same, over the years revisions and alterations were made by the creators, and over time by subsequent producers and directors. Some of these revisions were for length and some for convenience, as when a different actor played a certain role and was unable to perform a specialty piece written for the role's creator. Some have been made to reflect contemporary sensitivities toward race, gender and other social issues. In 1887, the show boat "Cotton Blossom" arrives at the river dock in Natchez, Mississippi. The Reconstruction era had ended a decade earlier, and white-dominated Southern legislatures have imposed racial segregation and Jim Crow rules.