Hyacinth Robinson, a young man and a skilled bookbinder, meets revolutionary Paul Muniment and gets involved in radical politics. One night in the theatre Hyacinth meets the radiantly beautiful Princess Casamassima, who has become a revolutionary herself and lives apart from her dull husband. Meanwhile, Hyacinth has committed himself to carrying out a terrorist assassination, though the exact time and place have not yet been specified to him, and soon hi finds himself between the love and the ideology.