Twelveness is based on the real friendship—and tennis rivalry—between two very different early 20th century composers: the respected but severe Arnold Schoenberg and the wildly popular George Gershwin, who sponsored Schoenberg’s family when they fled Nazi-era Vienna for the US.

Set in 1937 Los Angeles, the play features Schoenberg; Gershwin; Schoenberg's wife, Gertrud; and Gershwin's girlfriend, actress Ginger Rogers.

On the court and over dinner, these four mismatched friends and lovers debate the nature of artistic process and artistic inspiration.

Looming over the quartet is the fact that, unknown to them but known to the audience, Gershwin is suffering from a brain tumor that will take his life within a year.