In seventeenth-century England, Barbara Winslow helps her rebellious brother, Rupert, to escape the King's forces. Barbara is captured while disguised as Rupert, but Captain Prothero becomes enamored with her and sets her free. Later, when Barbara and the captain are imprisoned, they discover a secret passage that enables them and their fellow captives to escape. Barbara then secures a pardon for herself and the captain by revealing a plot against the king. Prothero is exiled from England, and Barbara goes with him.