Young widow AJ Sinclair has met her match when the Yellowstone supervolcano erupts. She and her nine-year-old autistic son, Will, embark on a risky road trip from Maine to the epicenter to find her other son who is missing. Along the way, they meet Reid Gregory, who travels his own road to perdition looking for his sister. Drawn together by AJ's fear of driving and Reid's military and local expertise, their journey is fraught with the chaotic aftermath of the eruption. AJ's anxiety and faith in humanity are put to the test as she heals her past, accepts her family's present, and embraces uncertainty as Will and Reid show her a world she had almost forgotten.