Kenzie and Quinn have been step-sisters and best friends since their parents married when they were two; being sisters is all they've ever known. But tension and constant screaming matches between their parents have left the girls lost and confused: there are no visitation rights for step-sisters and if their parents divorce, they're not sisters anymore. They're just ... nothing.
Recognizing the girls' roiling anxiety, their grandmother sweeps the sisters away for the summer, bringing them to her house on North Carolina's Outer Banks. While out kayaking, the pair come across three wild marsh ponies grazing just a few yards away! The girls stare in awe, talking in hushed whispers; the herd on these islands have lived here for hundreds of years, descendants of a Spanish shipwreck in the 16th century. One is a very, very pregnant mare, and the girls vow to spend their summer watching over the wild mare and her fragile newborn foal, which they name Starling.
They want to make the most of their last summer as sisters, but as Kenzi mourns the impending loss of her step-mother and Quinn comes to terms with the crush she has on her best friend back home ... it's hard to imagine saying goodbye. Whatever happens to Starling at the end of the summer, it's clear that things will never be the same.
