The full plot of The Batman (2022) is a chain of Riddler murders that exposes Gotham's corruption, the Wayne family's own part in it, and a flood that threatens the mayor-elect. Everything from here on is a spoiler.
The mayor's murder is only the first of several. The clues show that the mayor was having an affair and that many city officials take money from the crime boss Carmine Falcone. Batman and Selina Kyle meet while chasing the same leads, because her roommate Annika has vanished, and the two begin working toward the same answers. The Riddler then kills the police commissioner and kidnaps the district attorney, Gil Colson. Colson is fitted with a collar bomb, and the Riddler forces Batman to answer riddles to try to save him. Colson dies after refusing to name a police informant.
The Penguin is captured along the way, but he turns out not to be the informant. The trail instead runs to an orphanage once funded by the Wayne family, and Alfred is injured by a letter bomb. Evidence suggests that Bruce's father, Thomas Wayne, hired Falcone to silence a journalist, and that Falcone may have had Bruce's parents killed.
Selina learns that Falcone is her father and that he killed Annika. She tries to kill him, but Batman stops her, and Gordon arrests Falcone. The Riddler then shoots Falcone with a sniper rifle, gives himself up, and is unmasked as the forensic accountant Edward Nashton. He is sent to Arkham State Hospital.
His plan is not over, though. Car bombs he planted breach the seawall and flood the city, and his online followers go after the mayor-elect, Bella Reál. Batman and Selina stop the attack and help rescue people trapped in the flooded arena. Afterward Nashton befriends another inmate at Arkham, Selina leaves Gotham, and Batman decides to bring hope to the city instead of seeking vengeance.