Lord Cassius is Keefe's father, and part of the Sencen family. He worked for the council and is a powerful Empath. Lord Cassius's wife is Lady Gisela, who is the leader of the Neverseen. In Keeper of the Lost Cities, he meets Sophie briefly on the staircase leading down from the Level Four wing at Foxfire, at the end of Midterms celebration. He took quite an interest in Sophie, hinting that he knew she was the mystery prodigy that Sir Tiergan was mentoring. Lord Cassius has proved to be very selfish and vain even having a room filled with his accomplishments. Lord Cassius thinks Keefe should stop wasting his time and work harder in school. Lord Cassius wrote a book about Empathy, called The Heart of the Matter. Keefe, who had to read it in Book Four, described his father as a "torturer of innocent readers," but in later books, Keefe did say he learned a bit about head and heart emotions. He is not a great father and has constantly belittled his son.
His name, Cassius means "empty", or "vain", referring to his character.
Lord Cassius is described as a taller man with many of Keefe's characteristics, but with blonde, slicked back hair and neater attire.
- Lady Gisela (Wife/enemy)
- Keefe (son)
Lord Cassius does not have a strong relationship with his son. He constantly makes rude and sharp remarks about and to his son. He forced his son to live with him by threatening to withhold vital information that the Black Swan desperately needed. After a while he starts to care about Keefe forcing him to come with him to places even though Keefe still find his father annoying.
- Ro (annoyance)
Ro is Keefe's loyal ogre bodyguard. She spends some time with Lord Cassius and during that time almost always tried to insult him. She has called him multiple names, such as Lord Fancy Clothes and Lord Pretentious. She also has a name for his extraordinary beach house, Shores of Solace, calling it Waves of Wimpiness.
Sophie meets Keefe and Lord Cassius in the Level 4 wing at Foxfire. She notices that Keefe is always down when his father is there. Lord Cassius calls Tiergan an "infamous mentor" when he (Tiergan) saves Sophie from sharing her identity as a telepath.
After Sophie's telepathy is revealed to the public, Keefe describes his father as very smug. Apparently, he had guessed that Sophie was Tiergan's prodigy, and Keefe says that his father always has to be right, and he always is.
During Book 3: Everblaze, Keefe believes Lord Cassius works for the Neverseen, but it is Lady Gisela who is working for the evil organization. Lord Cassius was completely blind to the fact that she was manipulating him.
In Nightfall, Lord Cassius tells Keefe and Sophie where Vespera hid her signature in Atlantis, proving he is somewhat worthy to be a part of the Black Swan, which he later joins. It was said earlier that Fitz had suspected Lord Cassius to have been the one to break his wife out of jail, which is something Keefe severely doubts, stating that his father cares more about his reputation than to rescue her.