Ant-Man and the Wasp meet their friend Carol Danvers at a SHIELD funded observatory and are introduced to Dr. Phillip Lawson. Danvers and Lawson ask the two Avengers' opinion on a stellar object approaching Earth at speeds faster than any recorded comet. After the object smashes SHIELD's orbital telescopes and crash lands near their location, the Avengers and Danvers decide to investigate. Meanwhile, an unseen and dangerous force lurks in the woods surrounding the observatory.
When the Avengers and Danvers arrive at the crash site for the object, only to find nothing but a glowing crater, they begin to survey the area surrounding the crash. The trio are soon attacked by the invisible enemy, which is revealed to be a towering extraterrestrial robot. After a brief battle, the robot sets it sights on the observatory. Upon arriving, it attempts to destroy the power source of the building. In the attack, the robot inadvertently reveals that Dr. Lawson is an alien known as Mar-Vell. During the battle, Carol Danvers is knocked out and rushed to the hospital.
Several other members of the Avengers meet Ant-Man, the Wasp and Captain Mar-Vell at the hospital that Carol Danvers was taken to. Mar-Vell explains to them that his race, the Kree, have been at war with another alien race known as the Skrull. During their intergalactic conflict, both sides have begun seeking out planets of either strategic significance or rare resources. The robot that was sent to earth is a Kree Sentry Drone, an intelligent weapon designed to "defang" planets that the Kree deem worth conquering in their ongoing struggle with the Skrull. More distressingly, each Sentry Drone is armed with a "negabomb" capable of eliminating extremely dangerous species. Unfortunately, due to this Sentry's rather violent first encounter with Earth, Mar-Vell fears that it is only a matter of time before the negabomb is detonated.
The Avengers, with the help of Captain Mar-Vell, track down the Sentry in hopes of deactivating the bomb before it explodes. Initially the Sentry is able to fight off the combined efforts of the heroes. At one point, Ant-Man protects the Wasp from a missile barrage, nearly professing his love before passing out from his own injuries. Enraged, the Wasp flew into the "mind" of the robot, destroying major circuits before finding the negabomb. A holographic projection of Mar-Vell's commander, Yon-Rogg, appears from the Sentry and declares that Earth is to be considered Kree space, no matter if humans survive...or Mar-Vell. With that, the Negabomb is activated. Without enough time to defuse the bomb before it explodes, Mar-Vell and Avengers fling the negabomb into space to explode safely, far away from Earth.
Back at the hospital, Ant-Man is recovering in the same hospital room as Danvers. Mar-Vell warns the Avengers that the Kree are not going to give up their conquest of Earth; he plans to leave Earth to argue to the Kree leader, the Supreme Intelligence, to spare the planet, but still warns the Avengers to prepare for "the storm that is coming." Soon, Ant-Man recovers from his injuries. When prompted to finish what he was saying before he passed out earlier, he stammers until he is cut off by Carol Danvers. She has also recovered from her injuries...and is levitating several feet above her bed.