The story is based on a real story of the residents of the island of Miyakejima, which erupted in 2000 and had to be evacuated.A family, Matsuo, Takako, Matsuo's mother Fusako, and Matsuo and Takako's young son Shin live on the island of Miyakejima, 200 km south of Tokyo. Together, they run a small bed and breakfast for tourists and have two pet golden retrievers, Hana and her son Rock. Shin is in charge of taking care of Rock every day, and despite some typical rambunctiousness from Rock (including peeing on Takako on multiple occasions), they lead a happy life. However, Hana becomes ill, consuming Fusako's attention, and the island starts to be hit by multiple earthquakes, causing visitors to cancel their reservations at the inn.Soon they find out the source of the earthquakes - the island's volcano is erupting. The family initially don't want to evacuate because they have lived on the island their whole lives. But after a while, with the whole island covered in ash, the residents decide to send the children off to Tokyo for school to keep them safe. Shin doesn't want to leave his parents and Rock, who he has promised be with, but he has no choice.Soon after, Hana dies, leaving Fusako distraught. As the volcano gets worse and worse, the rest of the family has no choice but to evacuate, which upsets Takako because she is afraid they will never return to the island. They pack up, however, and put Rock in a crate to take with them on the ferry to the mainland. However, right before being loaded on the ferry Rock breaks out of his cage and the handlers are unable to find him before the ferry leaves.Soon, Fusako, Takako, and Matsuo arrive in Tokyo, to find out Rock was left behind. Matsuo telephones the dorm that Shin is staying at and tells him what happened, greatly upsetting Shin. Matsuo says he doesn't know if Rock is alive or dead, but promises that they will go back to the island and do everything they can to look. Fusako, Takako, and Matsuo set up a small one room apartment in Tokyo, and get part time jobs to earn money to go back to Miyakejima when they can. Shin spends his free time visiting a rescue center for animals from Miyakejima, hoping that Rock will turn up. Fusako decides to move out on her own so that there will be room for Shin to live with his parents, and the whole family tries to adjust to Tokyo life.At a street fair for the residents of Miyakejima, Shin hears that they have started to let some residents make short visits to the island, and that someone found a large dog that might be Rock. The family gets a phone call that the dog has been taken to the animal rescue center, and they go there to find Rock, dirty, injured, and unconscious, but still alive. However, since they live in such a small apartment, they are forced to leave him at the center, and while Rock initially recovers he gets sick from the stress of living in the small space at the shelter. Shin is determined that they will get Rock back when they go back to the island, but other kids who were displaced from the island are pessimistic that they will ever be able to go back.Matsuo is allowed a short visit to the island, and while wearing a face mask, reviews the damage to his family's home/bed and breakfast. It's partially collapsed and under several centimeters of volcanic ash. Another resident who has made the journey with him, a family friend named Fuku, collapses when seeing the damage and never wakes up again. Matsuo is now unsure that they will ever be able to go back, but he promised Shin that they would one day.Shin decides that he needs to do the right thing by Rock, and allow the rescue shelter to find a new home for Rock, because they will probably never be able to take him back and go back to the island. However, after he signs the paper allowing an older couple to adopt Rock, and then leaves, his father asks the couple if they could just take care of Rock instead of adopting him, in the hopes that they can one day take him back.Five years after the volcanic eruption, the residents are told that they can finally return to Miyakejima. Shin is now in middle school. Matsuo finds the vet who was at the animal rescue center and asks how to get back Rock. The vet tells him that such a long time has passed, and the couple renamed Rock, and would Rock remember Shin? Matsuo replies that Shin is sure that Rock will remember him. They arrange a reunion, and sure enough, Rock does remember Shin.The family goes back to Miyakejima, to find their family home still in horrible condition. The movie ends with all the family members happily repairing their home, together again at last.