In the spring of 1986, a catastrophic explosion occurs in a certain nuclear plant, leading to the arrival of a mysterious girl named Mimi in a quaint village in Western Finland. Instantly, Mimi brings a certain warmth and brightness into the life of 15-year-old Mariia. Two decades later, Mariia comes back home to care for her ailing mother, prompting a flood of memories from that significant summer to resurface.