The Fithling Scientist that appears in Kingdom of Liars is a major antagonist in the series. He was employed by an assassin who was hired to assassinate Sir Brandt, a nobleman and retired general of Ashbane. The assassin hired the Fithling Scientist to design a weapon that would kill Brandt. Brandt was supposed to be on the same train as the unnamed protagonist and his sister, but instead, his brother was on it, and died along with everyone else. The Fithling Scientist's henchmen were killed with that very weapon and the Fithling Scientist locked himself inside his lab. The hero manages to get inside and get some information out of him. The Fithling Scientist is currently in prison.
- It is revealed that all Fithling Scientists must wear their helmets or else they die
- This may be the same Fithling Scientist as the one that appears in Hood, but that is yet to be determined