In a secret lair, a mysterious figure contemplates a scale battlefield and places a toy soldier on horseback as he speaks the rhyme from "Humpty Dumpty."
On the streets of Gotham, pedestrians notice a giant toy soldier on horseback standing on the street. The police pull up and order them away, and then call in a report. The toy soldier comes to "life" and opens fire on the two policemen. They return fire, causing the robot to explode. As they approach it, a person inside begs them to help.
Lt. Gordon is called to the scene and tells the officers to pry the prisoner out with the jaws of life. However, Batman arrives and orders them to stop. He tosses down a batarang which scans the toy soldier. The vigilante then warns Gordon that the suit is a bomb, capable of wiping out the entire block. Gordon tells the officers to arrest Batman, but when they turn back, he's gone. The lieutenant has no choice but to call in the bomb squad.
At Wayne Manor, Tatsu goes back to recover the Soultaker from where she hid it. Alfred comes up and asks what she's looking for, and she claims that she's looking for her keys. Tatsu says that they'll turn up and makes a hasty exit.
Beneath police headquarters, Gordon watches as the bomb squad tries to cut open the suit. Batman hacks Gordon's phone and calls him, having confirmed the imprisoned man is Icepick Joe. Joe is a hitman for Tobias Whale, and Gordon warns Batman to stay away from the mob boss. Batman says that he can't and signs off, and then goes to a warehouse belonging to Tobias. The vigilante drops in on Tobias and asks what happened to Icepick Joe, and Tobias says that he disappeared and figured Batman had captured him. Tobias's men attack Batman, who easily takes them down. By the time he gets to the mobster's office, he discovers that Tobias has been taken away. Sitting on the table is a toy soldier.
In his secret lair, the villain responsible for the explosive suits positions his toy soldiers on a battlefield, aiming cannons at each other.
A taxi driver discovers two giant toy soldiers on the street, aiming cannons at each other. As the people inside call for help, the suits activate and light the cannons. Batman arrives and throws two batarangs into the nearby lampposts, bringing them down and deflecting the cannonballs.
At police headquarters, Gordon is in his office when Batman slips in and warns the lieutenant that someone is sending Gotham a message. He gives Gordon a file on Tobias' chief financial advisor, Donovan Baker, and DA Marion Grange. The two men were in the newest toy soldier suits. Batman informs Gordon that Tobias has gone missing and figures that there's a connection. Gordon says that they're all tied together by the Dumpler case. Mob accountant Dumpler was going to testify against Tobias, but the mobster had one of his men fire a missile at the witness, injuring him. Dumpler went crazy and escaped protective custody, disappearing until now. Batman warns that Dumpler will come after Gordon next, holding him responsible for what happened, but Gordon insists that he can take care of himself.
At Wayne Manor, Tatsu continues searching for the Soultaker. She realizes that she has no choice and goes to see Alfred in the kitchen. When Tatsu asks for his help, Alfred shows her the sword where he's keeping it in his office. He refers to it by name and asks Tatsu how she obtained it.
Gordon is at home going over his files as Batman watches from nearby. Barbara Gordon comes home and finds a toy soldier on the kitchen table. Batman, listening in, realizes that Dumpler is in the house. As the vigilante runs for the house, three toy soldiers roll out and open fire on him. Batman ducks out of the way and they open fire, and Batman realizes that there is no one inside of the suits.
The lights go on inside the house and Gordon tells Barbara to get out the back. She does, but finds Dumpler waiting for her, dressed as the nursery-rhyme Humpty Dumpty. Dumpler grabs her and slaps Gordon aside. By the time Batman disables the toy soldiers and runs inside, Dumpler has left with Gordon, leaving Barbara behind.
Batman drives out and queries his computer on Dumpler's last known address. The house is demolished but Dumpler's grandmother died under mysterious circumstances. Batman heads for the grandmother's address, an older home, and breaks in. He finds the room with the battlefield and the toy soldiers lined up in front of a castle. There's also a workshop with explosive suits, and Batman identifies the frequency that will nullify the arming signal.
At Wayne Manor, Alfred takes Tatsu to the hidden elevator and down to the library. He explains that his old employers in MI6 were looking for the Soultaker, and finds a book showing the sword's wielder taking the souls of his victims. Tatsu assures him that the legends are true and remembers when she saw Silver Monkey use the sword to kill a victim. She was working undercover for the CIA, joining the League of Assassins to find Ra's al Ghul. Rather than let the League hold the sword or hand it over to the CIA, Tatsu took it and went into hiding. Alfred wonders why they're still alive if the League knows that the Soultaker is at Wayne Manor.
At Dumpler's new home, Batman programs his batarangs with the counter-frequency and then realizes the significance of the model castle. He drives to its real-life counterpart and finds toy soldiers on the field outside. Dumpler is on the wall, armed with a machinegun, and opens fire. There are dozens of toy soldiers, and Dumpler boasts that most of them are empty. Batman continues his way through the battlefield, disabling soldiers until he finds the one with Tobias inside. He gets the mobster to the Batmobile, and Tobias runs off rather than risk himself.
Batman goes back and finds Gordon, and a furious Dumpler fires on him. The vigilante tells him that it's time to stop, but Dumpler continues firing at the Batmobile. Batman charges toward him and gets close enough to scale the castle walls. Dumpler flees into the castle, insisting that it's not his fault that they dragged him into their war. He runs up the stairs of the highest tower and Batman goes after him, insisting that it has to stop. When Batman gets to the top, he finds Dumpler standing on the battlement. He falls off and hits the ground far below... and shatters into metal pieces.
As Batman goes back to the Batmobile, Gordon gets a radio call that all of the suits deactivated. When he wonders why, Batman suggests that Humpty is broke but not evil, and he retired from the field of battle honorably when he lost. However, he's sure that the war will continue.