Assassin's Creed: Underworld is a novel written by Oliver Bowden starring Henry "the Ghost" Green as a companion to Assassin's Creed: Syndicate, during the construction of Britain's first underground railroad in 1862. It was released on December 1, 2015 in the US and November 5, 2015 in the UK.
Jayadeep Mir is the son of Arbaaz Mir and Pyara Kaur. Born and raised an Assassin from his birth, he had a promising career but in the words of his mentor, Ethan Frye, he did not yet have the killer instinct. His first assignment proves a disaster and in disgrace, he's exiled to England where he takes on a series of aliases as he infiltrates the lower depths of the city. "Henry Green" becomes the linchpin of the Assassin network in London meeting the likes of Frederick Abberline, Alexander Graham Bell, Charles and Mary Pearson as he tries to keep up to speed with the Templars.
- A Day in the Limelight: Underworld stars Henry Green, The Mentor of the Frye Twins and leader of the British Assassins, before the events of Syndicate.
- Deliberate Values Dissonance: The Indian Assassins are a little more medieval and pre-Altair than other branches. Arbaaz Mir even feels that Ethan Frye and the British Assassins are too soft, though that might be because Hamid from Assassin's Creed: Brahman is still The Mentor.
- The Exile: Ethan arranges this for Jayadeep. Arbaaz agrees and even fakes Jayadeep's death so that he can come to England and take a new name and identity.
- Gaining the Will to Kill: What a true Assassin needs as per Ethan Frye when he dresses down Henry for messing up his assignment:Ethan Frye: What did I always tell you? What did your father always advise? You hesitate, you die its as simple as that. An assassination is not a cerebral act. It requires great thought, but all of that thought goes into the planning and preparation, the contemplation and visualization prior to the act itself. That is the time for second, third, fourth thoughts, as many thoughts as you need until you are sure absolutely certain that you are ready to do what needs to be done. Because when you are in the moment, when you stand before your target, there is no time for hesitation.
- Good Parents: Jayadeep's parents are this to him as a child and after some Character Development, Ethan Frye resolves to become this his twin children.
- Ignored Expert: Ethan warned Arbaaz that Jayadeep wasn't ready for the assignment, but Arbaaz ignored and Jayadeep failed just as Ethan predicted. Indeed, Ethan actually planned to save his former student's life by bringing the letters he had sent to Arbaaz before the Council and blaming the father for his son's failure but was relieved that it didn't come to that.
- Jock Dad, Nerd Son: Arbaaz Mir wants Jayadeep to be a warrior and trains him accordingly but Ethan Frye states that the future Henry Green lacks the "killer instinct" and Arbaaz sends an unprepared novice in the field despite Ethan's recommendation that Jayadeep makes a better planner and bureaucrat than field agent.
- Like a Son to Me: Ethan Frye likes Henry Green nearly as much as he likes his own kids and Henry comes to see Ethan as a father figure especially when his own father feels disappointed in his son.
- The Mentor: Ethan Frye to Henry Green.
- Noodle Incident: Ethan Frye and Arbaaz Mir first met in an adventure concerning the Koh-I-Noor Diamond. Apparently it's the same as the one in Assassin's Creed Chronicles: India since it concerns William Sleeman and Alexander Burnes.
- Prequel: Takes place in 1862, about six years before Syndicate's main story. The second half of the book retells the events of Syndicate before ending with the Pressed Flowers cutscene of Henry proposing to Evie.
- Switching P.O.V.: Unlike the previous three novels which were epistolary journals written in first person, Underworld employs a switching POV following at several times, Ethan, Henry and Frederick Abberline. And later, Evie Frye.
- Took a Level in Jerkass: Arbaaz, the roguish young layabout from Brahman has become a Blood Knight Proud Warrior Race Guy by the time of this story. He loves his son but he refuses to consider that he was mistaken in his upbringing or that he was endangering his life by forcing him in a situation he wasn't ready for.
- Victorian London: Much like Syndicate it takes place during this era.
- "Well Done, Son!" Guy: Arbaaz and Jayadeep used to be pretty close growing up but after the failure of the assignment, they become very estranged.
- Wretched Hive: Underworld is set in the seedier part of London and describes poverty of the time far more realistically than what we see in the main game.