The full story
After the events of Infinity War, Ant-Man and the Wasp presents a smaller-scale story about family and second chances.
Scott Lang has been under house arrest for two years as punishment for violating the Sokovia Accords by helping Captain America in Germany. He has three days left on his sentence. He has been a model prisoner, building elaborate cardboard mazes for his daughter Cassie and learning close-up magic. He has not contacted Hank Pym or Hope van Dyne, who are also fugitives because of him.
Then Scott has a vision of Janet van Dyne, Hank's wife, lost in the Quantum Realm for thirty years. His brief trip to that subatomic dimension in the first film created a quantum entanglement with her. Janet is alive, and she's using Scott to send a message.
Hank and Hope have been building a tunnel to the Quantum Realm. With Scott's connection to Janet, they can finally pinpoint her location. But they need a component from black market dealer Sonny Burch, and they're not the only ones after Hank's technology.
Ghost—real name Ava Starr—phases through solid matter, a condition that is slowly killing her. She was caught in a quantum explosion as a child, the result of an experiment gone wrong. S.H.I.E.L.D. weaponized her for years, promising a cure that never came. Now she wants Hank's technology to stabilize herself, even if it means trapping Janet in the Quantum Realm forever.
The film alternates between chase sequences, size-changing effects, and personal drama. Luis and his crew return. Scott and Hope work together throughout. Hank's guilt over Janet's sacrifice—sending her into the Quantum Realm to stop a Soviet missile—reaches resolution.
They rescue Janet. She has been surviving in the Quantum Realm for decades, evolving and gaining quantum healing powers. She stabilizes Ava, giving her a future. The family reunites.
In the mid-credits scene, Scott enters the Quantum Realm to collect healing particles for Ava. Hank, Janet, and Hope are on communication, ready to bring him back. Then silence. Scott calls for extraction. No response. He is trapped in the Quantum Realm as the camera pulls back to show Hank, Janet, and Hope disintegrating into ash.
Thanos snapped his fingers. Half the universe is gone, and Scott Lang is stuck in a dimension outside normal space-time with no way home.
In the post-credits scene, back at Scott's house, the giant ant Hope left behind to fool his ankle monitor is playing his drum kit—the only sign of life in a house that's about to find out why no one's coming home.