"The Tale of Sir Gareth" in Sir Thomas Malory's Le Morte D'Arthur reveals both women's inferior position in society and their unofficial power.
Officially, women are social inferiors who must rely on the protection of men during the time in which this story is set. Lyonet, for instance, must come to Arthur's court to seek help for her sister, whose castle is besieged by the Red Knight. The sisters have no power to deal with the problem on their own. They are not warriors, and they have no legal recourse. They must rely on the generosity, prowess, and courage of Arthur and his knights.
Further, Lyonet is not at all happy with Arthur's selection of her champion. In her eyes, he is merely a kitchen boy, nicknamed Beaumains but actually Gareth in disguise, who has asked for the job. But again, she has no choice in the matter and must go along with the king's decision.
Women are also used as tools in this tale. When Gareth defeats Sir Persaunt, he and Lyonet (who has been reluctantly traveling with him, again without much of a choice) stay the night with Sir Persaunt. The knight sends his daughter to attempt to seduce Gareth and thereby bring him under Sir Persaunt's control. Gareth refuses the lady and will not violate her honor, caring far more about her than her father apparently does.
For all their social inferiority, however, women do have quite a bit of unofficial power in this tale. Gareth gives Lyonet the authority to determine when he will and will not show mercy to another knight. Later, she stops him from sparring with his own brother, for these knights are gallant and will not refuse a lady's request. Notice, too, how quickly Arthur responds to Lyonet's plea for help.
Lyonet's sister, Lyonesse, falls in love with Gareth and has the power to send him on a year-long quest, apparently to further prove himself. She also requests that Arthur declare a tournament at her castle with the winner receiving her hand in marriage. Arthur is quick to grant this favor. Lyonesse provides Gareth with a magic ring, and she eventually marries exactly the man she wants: Gareth himself.