As Scott Lang balances being both a superhero and a father, Hope van Dyne and Dr. Hank Pym present an urgent new mission that finds the Ant-Man fighting alongside The Wasp to uncover secrets from their past. Scott Lang is under house arrest and spends his days with his daughter Cassie. After having a dream about Janet Van Dyne, Scott receives a call from Hank Pym and Hope van Dyne who need his help to rescue Janet from the Quantum Realm. Together, they battle a new enemy named Ghost, who can phase through objects. Along the way, they face challenges, including a black-market dealer and the FBI. They eventually succeed in rescuing Janet and restoring her to her family. However, during Scott's attempt to return from the Quantum Realm, he is left trapped when Hank, Janet, and Hope are killed by Thanos. The film ends with the world devastated by Thanos' snap, leaving Scott stranded in the Quantum Realm.

Scott Lang and Hope Van Dyne are trapped in the Quantum Realm with Hope's parents and Scott's daughter Cassie. They must find a way to escape while uncovering the secrets of Hope's mother and facing off against the mysterious Kang, a time-traveling adversary.

Armed with a super-suit that can shrink and increase his strength, Scott Lang must help his mentor, Dr. Hank Pym, execute a plan to save the world. However, he must first navigate the world of heists and superheroes to become the hero he is destined to be.