After poleaxing his mathematics master with a perfect right, Cashel Byron, the unloved son of a successful actress, runs away to Australia. He returns to England and becomes the most famous prizefighter of his age, only to be floored himself by the lovely and impossible Lydia Carew.

Can Lydia, with her reputation for vast learning and exquisite culture, be wooed by the ruffian Cashel? Can Cashel successfully hide his illegal professional? And so follows, with Shaw's inimitable wit and sparkle, a tale of miscommunication, drawing-room comedy and love.