Gotham: City of Monsters is the second tie-in novel to Gotham following Gotham: Dawn of Darkness. The title was confirmed by Jason Starr in April 2017, and was released on May 29, 2018. Its story takes place during the six-month gap in-between season 2 and season 3.
The official link between Gotham seasons two and three, revealing Jim Gordon's return to Gotham City to set himself up as a freelance bounty hunter.
Having left Gotham City at the end of season 2, to search for Leslie Thompkins, Jim Gordon returns alone to establish himself as a freelance bounty hunter. He seeks out the monsters that escaped from Arkham Asylum and have aligned with Fish Mooney, now a metahuman herself. His return will have a direct impact on Selina Kyle ("Cat"), who also has decided to work for Fish, and becomes embroiled in events that may get her killed. Meanwhile Harvey Bullock is the acting police captain, and though he grows into the role, he hates it. When Gordon refuses to return to the force, this causes Bullock to question his loyalties.