Plot

Armed with a super-suit with the astonishing ability to shrink in scale but increase in strength, cat burglar Scott Lang must embrace his inner hero and help his mentor, Dr. Hank Pym, pull off a plan that will save the world.

Armed with the astonishing ability to shrink in scale but increase in strength, con-man Scott Lang must embrace his inner-hero and help his mentor, Dr. Hank Pym, protect the secret behind his spectacular Ant-Man suit from a new generation of towering threats. Against seemingly insurmountable obstacles, Pym and Lang must plan and pull off a heist that will save the world.—@PtotheSmizzo

After serving a few years in prison, former burglar Scott Lang is released. Now wanting to be straight, Scott sets out to find himself a job. But he is totally unaware that his record is preventing him from working and seeing his young daughter Cassie. When he steals a powerful suit, he quickly returns it only to find himself arrested again. But a mysterious man named Hank Pym has other ideas for him. Pym explains that it has the power to shrink in size and increase in strength due to a special formula called the Pym Particle. He was once its owner and called himself Ant-Man. Unfortunately during his SHIELD days, Pym discovers that others wanted to replicate his design. Now Pym wants to use Scott to being the new Ant-Man because his former apprentice Darren Cross is working to replicate the formula for his own evil purposes. So Scott and Pym, along with Pym's daughter Hope must plan a heist that will stop Cross and save the world from certain chaos.—Blazer346

A con artist named Scott Lang (Paul Rudd) gets a shot at redemption when his mentor (Michael Douglas) asks him to protect a super-powered suit. Donning the stunning technology, which shrinks him down to minuscule size, he fights off villains seeking to steal the invention, and organizes a heist that could save the world.

Ex-convict and recidivist burglar Scott Lang is recruited by Dr. Hank Pym to don the Ant-Man suit - which grants him the mind-boggling ability to shrink in size while retaining his full strength. Pym - the original Ant-Man - trains Scott to use the suit, and plans a heist to stop his former protégé - Darren Cross - from weaponizing similar shrinking technology. Cross - now operating under the villainous "Yellowjacket" banner - threatens global security with his extremely dangerous innovations. But Scott teams up with Dr. Pym and his daughter - Hope van Dyne - to infiltrate Cross's lab so as to prevent the subatomic technology from falling into the wrong hands. In a final showdown, Scott defeats the wicked Yellowjacket by shrinking to the quantum realm and returning once more as the perplexing Ant-Man.—Zeger DESMEDT

In 1989, scientist Hank Pym (Michael Douglas) resigns from S.H.I.E.L.D. (led by Howard (John Slattery) and Peggy (Hayley Atwell)) after discovering their attempt to replicate his Ant-Man shrinking technology. Believing the technology is dangerous, Pym vows to hide it as long as he lives. Mitchell Carson wanted to force Hank to surrender the technology but is stopped by Howard and Peggy. Pym had developed the Pym particle which reduces the distance between atoms while increasing density and strength.

In the present day, Pym's estranged daughter, Hope Van Dyne (Evangeline Lilly), and former protege, Darren Cross (Corey Stoll), 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. The Yellowjacket is a highly weapon laden version of his own shrinking suit and can have devastating consequences, if put into production. Unknown to Darren, Hope is spying for Pym and wants Pym to give her his original suit to defeat Darren. But Pym steadily refuses to do that & asks Hope to consider his suggested alternative. However, Darren is having difficulty in achieving a stable molecular reduction, leading to his organic test subjects being reduced to a gooey mass of cells. Eventually, he succeeds.

Upon his release from prison, well-meaning thief Scott Lang (Paul Rudd) moves in with his old cellmate, Luis (Michael Pena). Luis's roommates are Kurt (David Dastmalchian), who is a computer wizard & Dave (Tip "T.I." Harris) a pro lock smith. Lang has a master's in electrical engineering and yet cannot land a job due to his past record and has to serve at a Baskin Robbins. While visiting his daughter Cassie (Abby Ryder Fortson) unannounced, Lang is rebuked by his former wife Maggie (Judy Greer) and her police-detective fiance, Paxton (Bobby Cannavale), for not providing child support. Maggie asks Lang to get an apartment and to pay child support before he is allowed his visitation rights with Cassie.

Unable to hold a job because of his criminal record (Lang lies about his past to get the job but is fired whenever his background check is completed), 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. Unknown to Lang, the entire burglary was being observed by an ant with a micro-camera on it, which was relaying a live feed to Pym. After trying the suit on, Lang accidentally shrinks himself to the size of an insect. Terrified by the experience (during which Pym speaks to Lang via his helmet), 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 with the assistance of ants and flying insects.

At his home, Pym, who manipulated Lang through an unknowing Luis into stealing the suit as a test, wants Lang to become the new Ant-Man to steal the Yellowjacket from Cross. Pym says that he generates Electro-magnetic waves to stimulate the ant's olfactory nerves and is thus able to speak to them and get them to obey his commands.

Hope still believes that she can defeat Darren, but Pym is afraid to lose her as he did her mother. Pym explains to Lang that he designed a formula 40 years ago to shrink humans inside his suit. But he hid the formula as it was dangerous. He started his own company, Pym tech, & took Darren on as his protege. With time Darren suspected the existence of Pym's formula. When Pym did not cooperate with Darre, he voted Pym out of his own company.

Hope was angry with Pym for the death of her mother & helped Darren. But then she came back to Pym when she saw that Darren was loco. Pym's plan is to train Lang to use the suit & to break into Darren's lab, steal his suit & destroy all the data. Pym says that his specially designed helmet helps protect the brain chemistry, something that Darren has ignored in the design of his suit.

Having been spying on Cross after discovering his intentions, Hope helps Pym train Lang to fight in the suit and to control ants. While Hope harbors resentment towards Pym about her mother Janet's (Hayley Lovitt) death, he reveals that Janet, known as the Wasp, disappeared into a subatomic quantum realm to disable a Soviet nuclear missile (it was headed for the US and the only way to disable it was to go subatomic through solid titanium. Pym's own regulator was damaged, and so Janet stepped up). Pym warns Lang that he could suffer a similar fate if he overrides his suit's regulator. They send him to steal a device that will aid their heist from the Avengers' headquarters, where he briefly fights Sam Wilson/Falcon (Anthony Mackie).

Cross perfects the Yellowjacket and hosts an unveiling ceremony at Pym Technologies' headquarters. Lang, along with his crew and a swarm of flying ants, infiltrates the building during the event, sabotages the company's servers, and plants explosives. When he attempts to steal the Yellowjacket, he, along with Pym and Hope, are captured by Cross, who intends to sell both the Yellowjacket and Ant-Man suits to Hydra, led by former S.H.I.E.L.D officer Mitchell Carson (Martin Donovan). Lang breaks free and he and Hope dispatch most of the Hydra agents, though Carson is able to flee with a vial of Cross' particles. Lang pursues Cross as he escapes, while the explosives detonate, imploding the building.

Cross dons the Yellowjacket and attacks Lang before Lang is arrested by Paxton. His mind addled by the imperfect shrinking technology, Cross takes Cassie hostage to lure Lang into another fight. Lang overrides the regulator and shrinks to subatomic size to penetrate Cross' suit and sabotage it to shrink uncontrollably, killing Cross. Lang disappears into the quantum realm but manages to reverse the effects and returns to the macroscopic world.

In gratitude for Lang's heroism, Paxton covers for Lang to keep him out of prison. Seeing that Lang survived and returned from the quantum realm, Pym wonders if his wife is alive as well. Later, Lang meets up with Luis, who tells him that Wilson is looking for him.

In a mid-credits scene, Pym shows Van Dyne a new Wasp prototype suit and offers it to her. In a post-credits scene, Wilson and Steve Rogers have Bucky Barnes in their custody. Unable to contact Tony Stark because of "the accords", Wilson mentions that he knows someone who could help.