In 1989, scientist Hank Pym resigns from S.H.I.E.L.D. after discovering their attempt to replicate his Ant-Man shrinking technology. Believing the technology would be dangerous if replicated, Pym vows to hide it for as long as he lives. In the present day,[a] Pym's estranged daughter, Hope van Dyne, and former protégé, Darren Cross, have forced him out of his company, Pym Technologies. Cross is close to perfecting a shrinking suit of his own, the Yellowjacket, which horrifies Pym.
Upon his release from prison, well-meaning thief Scott Lang moves in with his old cellmate, Luis. Lang visits his daughter Cassie unannounced and is chastised by his former wife Maggie and her police-detective fiancé, Paxton, for not providing child support. Unable to hold down a job because of his criminal record, Lang agrees to join Luis' crew and commit a burglary. Lang breaks into a house and cracks its safe, but only finds what he believes to be an old motorcycle suit, which he takes home. After trying the suit on, Lang accidentally shrinks himself to the size of an insect. Terrified by the experience, he returns the suit to the house, but is arrested on the way out. Pym, the homeowner, visits Lang in jail and smuggles the suit into his cell to help him break out.