The Cornish Foundation is thriving under the directorship of Arthur Cornish when he and his beguiling wife, Maria Theotoky, decide to undertake a project worthy of the late art expert, collector, and notable eccentric Francis Cornish, whose vast fortune endows the Foundation. It is decided that the Foundation will fund the doctoral work of one Hulda Schnakenburg, a grumpy, remarkably unattractive, and extraordinarily talented music student. Her task is to complete the score of an unfinished opera by the Romantic composer E. T. A. Hoffmann. Additionally, and against all common sense, the Foundation will endeavor to stage the opera, entitled Arthur of Britain, or The Magnanimous Cuckold. The scholarly priest Simon Darcourt finds himself charged with writing the libretto.

As the production takes shape, complications both practical and emotional arise: the gypsy in Maria's blood rises with a vengeance; Darcourt stoops to petty crime; and various others indulge in perjury, blackmail, and other unsavory pursuits. Hoffman's dictum, "The lyre of Orpheus opens the door of the underworld," proves all too true—especially when the long-hidden secrets of Francis Cornish himself are finally revealed.