In the not-too-distant future, a small-scale nuclear weapon was created to wage aggressive, tactical wars. Amid the aftermath of a test of such armor going terribly wrong, residents of a paradise-like island must forever abandon their beautiful home.
Despite the grave danger, an 11-year-old Ava stays behind with her father Peter, who refuses to give up and instills in her true love of her land. Ava and Peter chose to adapt to the new reality, but while trying to save the slowly dying island, Peter dies.
Having just missed the final evacuation and now without a clear path to escape, Ava is left alone with her plushie toy Manta-Ray named Mr. Fish. She continues her father's work and learns how to survive on her own.
When out fishing one day, Ava gets tangled up in the fishing nets and almost drowns, losing Mr. Fish to the deep waters. Fortunately, a real majestic Manta-Ray comes to her rescue in all its grand beauty. Ava befriends the mysterious sea creature named Two Breaths that helps her cope with grief and loneliness.
When the danger of staying on the island grows, Ava must learn how to let go of the past and leave her home forever. Her chance to escape comes about when she sees a patrol boat off the island's coast. With encouragement from her Manta-Ray friend she swims for it.
The soldiers onboard the boat have orders to terminate everything from the exclusion zone. They aim their weapons at Ava and Two Breaths and stop just short of shooting... They drag Ava onboard but still try to execute the Manta-Ray...
When Ava finally peers over the stern, all she sees is her plushie Manta-Ray toy, Mr. Fish, sinking in the sea in the background of a dying paradise.