Trying to escape by helicopter with the Yellowjacket Suit, Darren Cross and HYDRA agents were chased by Scott Lang and ants controlled by him. During the chase, Ant-thony was killed by Cross. Lang managed to reach the helicopter, but Cross tried to kill him with a pistol, killing some HYDRA agents in the process. Cross asked Lang if he thought he could stop the future with a heist. Lang answered that it was never just a heist as Pym Technologies exploded and collapsed into the Quantum Realm.
Angered at the destruction, Cross put on the Yellowjacket Suit and started a fight with Lang. The pilots were killed in the midst of the fight and the damaged helicopter started to fall. During the fight, Lang and Cross fell into Cross's briefcase and got locked inside it before it fell from the helicopter, landing in the swimming pool of a neighboring home.
Cross returned to normal size and escaped from the briefcase. He threatened the resident family until Lang, also returned to normal size, stopped him. They continued their fight and Lang managed to swat Cross into a bug zapper. However, Jim Paxton and Gale appeared and subdued Lang, proceeding to arrest him.
While Scott Lang was taken away by Jim Paxton and Gale, Darren Cross was able to get inside Maggie Lang's house and take Cassie Lang hostage. Hearing of this prompted Lang to escape and battle Cross once again. With an army of ants as reinforcements, Lang engaged Cross on Cassie's toy train set. During the duel, Lang and Cross threw sections of the Thomas the Tank Engine toy at each other. As ants attacked Cross, Lang was able to knock Cross onto the train tracks, causing him to get run over by Thomas the Tank Engine. Cross retaliated by throwing the toy at Lang, but Lang knocked the train aside and onto the windowsill.
Back inside, Lang tried to use Pym Particles Disks to enlarge Cross but he deflected them, causing an ant living there and the toy train on the windowsill to grow to gigantic size. Paxton attempted to rescue Cassie, but the Giant Pet Ant trampled him on the stairs. Eventually, Paxton made it to Cassie and tried to protect her from Cross. In a last ditch effort to protect his beloved daughter, Lang decided to go subatomic to sabotage the Yellowjacket suit from the inside, causing Cross to shrink fatally into the Quantum Realm, finally killing him. Lang succeeded, but also became trapped in the Quantum Realm; however, he had an enlarging Pym Particles Disk remaining and used it to reverse the suit's mechanism, successfully returning to normal size.
As gratitude for Scott Lang's heroic act, Jim Paxton decided to wriggle him out of serving time and allowed him to see his daughter Cassie, who secretly kept the giant ant as her pet. They organized a family dinner where Paxton let Lang join his ex-wife Maggie and his daughter.