After the attack on the League of Villains, students in class 1-A return to U.S.J. to carry out rescue training under the supervision of Shota Aizawa and Thirteen, both in the process of recovering their injuries from the previous attack. What the students don't know is, before the training began, All Might told Shota that he wanted to add a surprise to the training, acting like a villain.
Shota originally was against the idea because the students had just experienced a villain attack, and All Might’s plan may traumatize them if it goes wrong. All Might replies that they must teach the students determination to overcome it, and teach them that they should always be prepared as heroes to face any threat. All Might eventually convinced Shota to let him add the surprise, but that it was to be his responsibility.
After carrying out rescue practices in the cliffside, the class moves to the urban area of the U.S.J. for another training, which involves of four students acting as rescuers, searching and helping their classmates in need of rescue scattered in unknown locations in unknown conditions. Thirteen selects Izuku, Ochaco, Minoru and Katsuki as the rescuers.
As the training starts, Katsuki blows himself away from the starting area in search of the victims. The remaining three agree to split up and search for the victims who are able to speak. Sitting in hiding, Shoto is founded by All Might. Shoto does not recognize All Might, and believing he is facing a true villain, he uses an ice attack against All Might, who dodges the attack and uncovers himself to reassure Shoto. Then All Might explains him his plan and ask to play along instead, acting as if he had been subdued by a villain. Shoto accepts.
Izuku, Ochako and Mineta are rescuing their peers. After Ochaco found Kyoka, Tenya appears and runs towards them, alerting them to take cover. Before Ochaco or Kyoka can understand what is happening, Tenya push them aside from a shock wave, which alerts the rest of the students. Ochaco asks what is happening, and Tenya replies that a villain has appeared. When the dust disperses, they see that the villain is holding an unconscious Shoto in one hand by his vest,
The other students arrive at the scene and are surprised to see what is happening. Mashirao runs to Shota and Thirteen for help, but they say they are too injured to fight, and Thirteen urges the students to run to the exit. The villain creates a large circular clearing within the urban area in a singular stomp to the ground, effectively trapping the students.
Thirteen tells the students to run away, but Katsuki runs into the clearing to fight the villain, and attacks him with his explosions, telling others to run if they want, because he is determined to defeat the villain. The villain strikes back, but Katsuki dodges him and manages to get behind him, eventually landing a solid hit on the villain's back, pushing him forward. Katsuki tells Tenya to tell the rest of the class to run away, calling them weaklings.
In response, the entire class shows their determination to fight. The villain praises his bravery, but generates a powerful shockwave that throws several rocks and debris at them, which are quickly destroyed by Yuga, Eijiro and Rikido. Kyoka uses his Earphone Jack to attack the villain, and while he holds the soundwave, Sero binds him with his tape while Momo creates a cannon to shot a net to restrain him, as the remainder of the class run at him. As the students approach, the villain breaks free and pushes all of them back.
Katsuki launches a surprise attack, but the villain easily holds him back. Izuku tells a few classmates about a plan he has concocted, and has Ochaco levitate him and Tsuyu launch him towards the villain with her tongue. Ochaco releases Izuku just as he uses one of Minoru's sticky spheres to pick up Shoto out of the villain's grasp. With Shoto released, Izuku attack the villain with a Delaware Smash, and stuns him long enough for Katsuki to launch a full power explosion at close range, propelling the villain onto a debris covered in Minoru's sticky spheres, entrapping him.
The students celebrate having caught the villain, and congratulate Izuku for his plan. Izuku returns the compliments, and says his plan worked because Katsuki understood his plan and followed until the end. As Katsuki approaches to deal the final blow, the villain takes off his mask, revealing himself to be All Might in disguise, surprising everyone.
Although All Might explains the reasons for their actions, the students yell at him, berating him that he went overboard. Shota and Thirteen watch the scene, knowing that the idea of All Might would end that way, but satisfied to see that the students would stand up to everything.
Shoto appears and apologizes to Izuku and Katsuki for being part of the surprise, having not been subdued by All Might but asked to play along instead. The students continue to berate All Might after he shows thanks to Izuku for restraining his upset towards him.