In some versions of Arthurian legend, Lynette (alternatively known as Linnet, Linette, Lynet, Lynette, Lyonet) is a haughty noble lady who travels to King Arthur's court seeking help for her beautiful sister Lyonesse (also Linesse, Lioness, Lionesse, Lyones, Lyonorr, Lyonors), whose lands are besieged by the Red Knight. The young Gareth picks up the quest, eventually marrying Lyonesse, while Lynette becomes the lady of his brother Gaheris.
They are most famously depicted by Thomas Malory in Le Morte d'Arthur, where they are sisters of Gringamore (Guinguemar) from Avalon. In Book IV: The Tale of Sir Gareth of Orkney, Dame Lynette comes to court asking for assistance against the Red Knight of the Red Lands. Since Lynette refuses to reveal her name for reasons which are not explained, she is presented with a kitchen servant instead of a champion. He says his name is Beaumains, but he is really King Arthur's nephew Gareth of Orkney in disguise. On their journey, the pair encounters the Black, Green, Red, and Blue Knights, and finally the Red Knight of the Red Lands (Sir Ironside). Gareth slays the Black Knight, incorporates the others into Arthur's court, and rescues Lynette's sister Lyonesse. Lustily in love with Lyonesse, Gareth conspires to consummate their relationship before marrying. Only by the magical intervention of Lynette is their tryst unsuccessful, thus preserving Gareth's virginity and, presumably, his standing with God.
Gareth later counsels Lyonesse to report to King Arthur and pretend she does not know where he is; instead, he tells her to announce a tournament of his knights against the Round Table. This allows Gareth to disguise himself and win honor by defeating his brother knights. The heralds eventually acknowledge that he is Sir Gareth right as he strikes down Sir Gawain, his brother, in a joust. The book ends with Gareth rejoining his fellow knights and marrying Lyonesse, in a joint wedding ceremony in which Gaheris marries Lynette and Agravain marries Laurel, Lyonesse and Lynette's niece.