Lady Isabel married the much older Baron of Tewsbarrow to save her family from a life of poverty. After the marriage, her husband tells her she must seduce his young nephew in order to produce an heir. The innocent Isabel knows nothing about seduction so the baron contrives a devious plot to make sure she succeeds. The young knight, Sir Daniel, is welcomed to his uncle's castle as an honored guest, but strange things happen. He realizes he's being drugged and while he lays helpless a beautiful woman comes to his bed. Despite the mystery surrounding her, Daniel falls in love. Then he learns Isabel's true identity and purpose and leaves Tewsbarrow with a broken heart. The old baron's plot fails, and he dies in a fit of apoplexy. Daniel returns as the new baron. His one burning desire is to punish the wicked woman who betrayed him.