Ten years have elapsed since a catastrophic solar flare obliterated the ozone layer, resulting in soaring temperatures of 150 degrees Fahrenheit (70 degrees Celsius) and transforming Earth into a nearly uninhabitable wasteland ravaged by ultraviolet radiation and extreme weather phenomena. Among the scant survivors is robotics engineer Finch Weinberg, who leads a solitary existence alongside his dog Goodyear and a helper-robot named Dewey in a subterranean laboratory located in St. Louis. This lab was once a property of the company where he worked prior to the global disaster. Finch's excursions to the outside world are limited to scavenging for supplies while clad in a specialized protective suit capable of withstanding heat and UV radiation.
As Finch grapples with an undisclosed illness—hinted at by his reading material on radiation poisoning—he dedicates his efforts to constructing a more sophisticated humanoid robot, intended to take care of Goodyear after his inevitable demise. To equip this new robot, which chooses the name Jeff, Finch imparts a wealth of encyclopedic knowledge, including a guide for the proper care and training of dogs. However, Goodyear remains skeptical of this new companion initially.
With the impending threat of a catastrophic 40-day storm sweeping toward St. Louis, Finch, along with Jeff, Dewey, and Goodyear, embarks on a hasty journey in a heavily modified motorhome towards San Francisco. Due to the urgency of their departure, only 72 percent of the data is uploaded to Jeff, leaving him with the cognitive capacity of a child. Despite his deteriorating health, Finch strives to impart crucial life lessons to Jeff, illustrating how to protect Goodyear. Jeff's curious nature presents both humorous and exasperating moments, and as he begins to exhibit more initiative, an unfortunate incident leads to Dewey's destruction. Their escape is further complicated by the pursuit of an unidentified vehicle.
As they near their destination, Finch experiences a significant moment when the UV radiation levels drop sufficiently, allowing him to embrace the sun’s rays without protection. During a tranquil afternoon, he teaches Jeff how to play fetch with Goodyear, an idyllic moment that foreshadows his quiet passing. In the aftermath, both Jeff and Goodyear venture into the now-deserted yet habitable San Francisco, setting out on a quest to locate any surviving humans that may remain.
