Brisienna Magnessen, also known as Lady Brisienna, is a sister of a great knight, and a high-ranking member of the Blades. She is the Grand Spymaster in the Iliac Bay region. She infiltrated the court of Daggerfall in the guise of one of the witches of Popudax.
When Nulfaga, the Queen Mother of Daggerfall, found the location of the Mantella, the heart that fueled the Numidium, the Emperor Uriel Septim VII sent a letter to the Queen of Daggerfall, Queen Mynisera. A special seal on the envelope was supposed to tip off Lady Brisienna that in fact the letter was intended for her. She was supposed to get the location of the Mantella by any means necessary. However, the War for Betony delayed the arrival of the letter. The letter arrived very late, after the war, and was received by Queen Aubk'i. Confused, the Queen sold the letter to King Gortwog in Orsinium.
When the ghost of King Lysandus haunted the streets of Daggerfall, the Emperor sent an agent to soothe Lysandus' soul, and at the same time get the controversial letter back. The agent arrived late due to a storm that wrecked his ship. Fortunately, Lady Brisienna managed to locate the agent and meet with him. She told the agent to investigate the three royal, dominating powers in the Iliac Bay region, Daggerfall, Sentinel, and Wayrest in order to know the reason of Lysandus's haunting and to procure the letter.
After the agent successfully soothed the soul of Lysandus and procured the letter, a mysterious friend told him the history of the Numidium. Soon later, all of the factions in the Iliac Bay region became aware that the agent was working to find the Mantella. Lady Brisienna meet the agent and asked for their help to get the Totem of Tiber Septim, which the Blades had lost. The agent found the totem in the Daggerfall vault. Then, more letters came to the agent, promising wealth and fame in exchange for the totem. Lady Brisienna had sent one of those letters.
In the end, after the agent recovered the Mantella, the Blades were then one of the wielders of the Numidium. The Empire's intelligence agency was one of the seven retrievers of the Totem of Tiber Septim, a tool for controlling the Dwemer construct.
Receive Lady Brisienna's letter and meet with her at an inn of her choosing.