At Wayne Industries, Bruce holds a press conference to announce his company's new ion cortex AI energy regulator. It will produce a global energy surplus within five years. Backstage, Katsu watches as Bruce calls out the man responsible, Dr. Jason Burr. Jason begins his speech but is interrupted when three ninjas drop down from the ceiling. They easily subdue the security guards while Katsu gets Burr and Bruce out. Burr trips and Bruce tells Katsu to guard Burr while he hides in the limo.
Katsu takes on and defeats three of the ninja, and the fourth one grabs Burr. Katsu disarms him and prepares to kill him with his own sword. Batman arrives and warns her that once she crosses the line, there's no going back. More ninja arrive and attack, and the heroes defeat all of them but one. The one ninja escapes and Katsu insists that it was necessary to kill them. Batman says that it wasn't and slips away. Eager to embrace his rescuer, Jason hugs Katsu. When they get to the limo, Bruce is inside and Jason gets in with him. Bruce explains that someone wants the ion cortex and offers to guard him at Wayne Manor. Jason agrees once Bruce assures him that Katsu won't leave his side.
The surviving ninja reports to his superior, Lady Shiva, who points out that a single woman fought him off. She tells him that the League of Assassins cannot overlook his failure and sends Silver Monkey to kill the man. Lady Shiva then tells Silver Monkey to recover Jason.
At Wayne Manor, Alfred assures Jason that there are heat sensors and alarms in every room. He shows Jason the panic room and the head of security, Mr. Reese, says that his team will keep him safe. Bruce comes in and tells Jason that Katsu will be staying with him while he goes to a museum reception with his date. Alfred goes with him and Bruce says that he's going to Jason's lab to see who might be after him.
Katsu and Jason are finally alone in the surveillance room and Jason tries to talk with her. She ignores him as best she can.
Batman enters the lab and discovers that someone has already broken in. He spots footprints on the floor and parries the swords of two assassins just in time. More move in and Batman holds them off. When he gets the upper hand, they disappear using smoke grenades and leave a bomb. Batman gets out just in time as the assassins drive away on motorcycles.
Jason talks about how his project will change the world and asks Katsu about her work. He jokingly asks if she'd have to kill him if she told him about her past, and she jokingly says that she would. Jason realizes that she's joking and they share a very brief laugh.
Batman pursues the assassins, gets ahead of them, and disables their tires. He grabs one killer and demands to know who sent them, and the assassin says that it's too late. Batman knocks him out and calls the manor.
Katsu checks the guest room and confirms that it's safe. Jason invites her to stay but she walks out. Meanwhile, Alfred tells Reese to lock down the property for the night. Reese goes outside and checks with his men at the gate. Once they turn their back on him, Reese darts them unconscious and two assassins jump over the wall.
Batman is unable to make contact with the manor. He tells the computer to contact Alfred via the commlink just as more assassins ride up on him.
Alfred gets the commlink signal and goes to the Batcave. Batman warns him that they're coming for Jason.
"Reese" removes his mask, revealing Silver Monkey. The assassin then goes into the manor.
Batman tells Alfred to initiate the fail-safe protocol and get Jason to the panic room. Alfred activates the system, unaware that Silver Monkey and his men are already in the building. Meanwhile, Jason is sleeping in his room when a figure enters the room and covers his mouth before he can yell. It's Katsu, who tells him that something is wrong. She puts pillows beneath the blankets and moves Jason down the hall to another room. Meanwhile, Silver Monkey enters the first bedroom and shoots a dart into the pillows. Katsu knocks him in, locks the door, and tells Jason to get to the panic room. As they run, Silver Monkey breaks through the door.
Batman tries to elude the assassins and consults his computer. It advises him to blow up the node on the top, disabling the lasers long enough to get inside. Batman continues to the manor and then brakes, knocking out the assassins as they shoot by. He then activates his glider unit, soaring off the road and toward the manor by air. Evading the missile barrage, Batman releases the glider unit, letting it slam into the node and buying him the seconds he needs to break through the ceiling and get into the manor.
As Katsu gets Jason through the dining room, Silver Monkey shoots more darts at them. Silver Monkey is surprised that Katsu is alive and Jason realizes that the killer knows her. The assassin promises that Katsu will die for her betrayal and attacks. The two of them fight and the killer draws a knife and prepares to kill her. Alfred shoots the knife out of Silver Monkey's hand, and the killer ducks and weaves out of the room.
Silver Monkey finds his remaining assassins on the roof just as Batman attacks. The assassin blinds him with a smoke pellet and leaves while his men distract Batman.
Alfred escorts Jason into the panic room, but Katsu seals the door behind them. She then goes to get the jade sword hidden in her room.
Batman disposes of the two assassins.
Alfred deactivates the fail-safe so that help can reach them. They check the outside monitor and discover that Silver Monkey has attached a bomb to the door. As he prepares to trigger the bomb, Katsu arrives and forces him to disarm the bomb. As he walks toward the door, Silver Monkey says that she's not worthy of the League of Assassins. He slashes her shoulder with a boot knife and sees the sword, and realizes that it survived as well. As he prepares to kill Katsu, Batman arrives and takes on the assassin. Silver Monkey kicks the charge off of the door onto the wall near Batman. When it goes off, it blasts a hole in the wall, allowing the killer to escape. As Batman goes after him, Katsu hides the sword.
Batman pursues Silver Monkey across the grounds and finally knocks him off the cliff. The killer throws another gas bomb, forcing Batman to let him go. By the time Batman regains his vision, there's no sign of the assassin. He climbs back up and Katsu offers her hand to help him up. She regrets killing Silver Monkey, but Batman tells her that Jason is safe and that she completed her mission. Jason runs up and tends to her wound, vowing not to let her die.
Silver Monkey returns to the League and informs Lady Shiva that Katsu is still alive. When she asks if he discovered anything else, Silver Monkey says that he found out nothing else. Lady Shiva says that they will let Jason live for now and recover the ion cortex later.