Myvryna Arano is a dunmer agent and member of the Thieves Guild living on the Waterfront. She is the one to deliver a secret invitation to you to join the guild.
She is actually a traitor to the guild and hired by Hieronymus Lex. After her cover is blown and the Thieves Guild frames her for the theft of Llathasa Indarys bust Lex arrests her despite the loyalty she’s shown him. While in prison she is strangely not given prisoner clothes and allowed to keep hers and allowed to keep a dagger.
Uzul gro-Grulam who lives in the same house as Myvryna expresses his interest in her and his thoughts of marrying her. During the theft of the Waterfront tax records they read that Myvryna is ‘exempt’, a possible early indicator of her work with Lex.