Darby doesn't understand how her mother, who grew up on Wild Horse Island, ever could have left. Now that Ellen Carter has come back to the island to visit, Darby hopes her mom won't want to leave again.

But Darby's grandfather and mother can't stop fighting, and Ellen wants to take her daughter back to California. When Darby finds a wild mare in the rain forest, she hatches a plan to convince her mom to stay - but will it work? Or will Darby have to leave the new home and wild horses she loves?