Cousins Coral and Isa are so close that they're practically siblings; their mothers are sisters, and the two girls grew up on the same small island. When Coral and her parents leave on a months-long sea voyage amid the islands of Indonesia, Isa is devastated that they'll be kept apart, and the two vow to write to each other no matter what.
Then the unthinkable happens, and Coral's boat capsizes at sea, where her parents and the rest of the crew vanish. Washed up on a deserted island, alone and wracked by grief, she must find the strength within to survive, and find her way back home. Meanwhile, Isa is still on Pebble Island, the only one holding out hope that her beloved cousin is still alive.