A young stranger drops in on the family of a prominent Italian industrialist and proceeds to seduce every member of the family, one by one. Such is the premise of Pier Paolo Pasolini’s Teorema (Theorem), released as a novel as well as a movie in 1968. Not surprisingly, the material checked a lot of boxes with Hans Werner Henze (1926–2012), who fled the homophobia and go-go postwar capitalism of his native Germany for the life of a champagne Marxist on the outskirts of Rome. A composer of dazzling gifts, fluent in all manner of international styles, Henze acquired the relevant rights to Teorema but assigned them to the rising Italian experimentalist Giorgio Battistelli (born 1953). In 1992, Batistelli premiered a characteristically oddball chamber opera for mute actors. Three decades grayer, Battistelli has now expanded Teorema into a full-length opera, scored for a large singing cast and large orchestra. Mimes double many of the principal roles, but not that of the anarchic Stranger—or Ospite (Guest)—played by Nikolay Borchev, a baritone in high international demand. —Matthew Gurewitsch