Darby Carter loves horses, even though she's never actually ridden one. Darby's grandfather is an expert rider—in fact, he owns a horse ranch in Hawaii. So when he agrees to take her in—along with the beautiful mustang Darby saved on the range in Nevada—she knows she can't refuse, even if she is a little terrified! But Darby's filly arrives in bad shape, and Darby's grandfather wonders if the wild horse will ever trust a human again. Can Darby take the reins and save her horse—or has she lost the mustang forever?

Ever since Darby rescued her wild filly mustang, she's been having a tough time at her grandfather's ranch. And after she accidentally endangers one of his loyal and steady horses, she can't help but wonder if she really belongs on a horse ranch at all. But then a shadowy horse shows up, prowling the grounds at night. Could it be the legendary Shining Stallion of Hawaii? And why is Darby the only one who has seen him? One thing is When the mysterious stallion sets out to challenge the wrong horse, only Darby can stop him—before anyone gets hurt.

Darby wants to visit her great-grandmother, a mysterious healer who lives in the middle of the rain forest. But she's afraid of the dark woods—until she sees a beautiful, elusive pink roan mustang roaming the forest. When Darby finally braves the forest and meets her new neighbors, she uncovers a secret tragedy—one that led to a terrible fight between her two best friends. Can Darby and her great-grandmother mend a broken friendship? Or will the rain forest mustang save the day?

Darby is nervous about starting at her new school in Hawaii, and when she gets there it's even worse than she thought. Within the first week she's made an enemy—her stuck-up cousin from the other side of the island. At least Darby has a new horse to go home a beautiful colt that she found abandoned on a remote beach. Darby loves the colt, and she knows he needs a good home. But when her new worst enemy's parents call to rescue him, will Darby be able to let him go?

Darby is excited to go on a "volcano watch," camping out and observing the island's volcanoes, despite recent small earthquakes that could mean an eruption is coming. After all, Darby grew up in California, so she's used to the earth rumbling now and then. Plus, the expedition is perfect for working with Hoku, helping the young mustang learn to handle any situation. But when the volcanoes do erupt, it's much scarier than Darby anticipated, and a stream of lava leaves Darby and Hoku stranded. Can Darby's horse-charming skills keep the mustang calm? Or will her filly run back to the wild?

When an earthquake sets off a tsunami on the shores of Wild Horse Island, the mustangs of Crimson Vale are chased by the waves and left stranded on a dangerous hilltop. Darby knows the lead mare, Medusa, will do anything to save her herd—but will she let the ranch hands bring her to safety? Or is it up to Darby to save Medusa and her band—before they're lost forever?

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?

After a tsunami washes over her Hawaiian island home, Darby Carter must pitch in to help get her grandfather's ranch back in order and make sure none of the horses drink contaminated water. Darby's friend Cade has even bigger worries. His mother, Dee, hasn't been seen since the storm. With no other leads, Darby and Cade set out in search of Honi, Dee's beloved pony. But even if they can find Honi, will she be able to take them to Dee?

Black Lava and his herd have been driven up to Sky Mountain to keep them away from polluted water. But there's only room for one lead horse on the mountain, and Snowfire, the white stallion, has already claimed it as his own. Sure enough, Darby soon sees Snowfire chase Black Lava onto ranch lands. Her horse charmer sense tells her the Crimson Vale herd needs to return home or desperation will lead Black Lava into more danger. Between finals at school and an upcoming rodeo, everyone is too busy to listen to Darby's fears. Can Darby help Snowfire and Black Lava before their battle turns deadly?

When Darby moves her mustang, Hoku, in with the other horses, Hoku starts acting wild again, and then her abusive former owner, Shan Stonerow, decides that he wants her back, threatening Darby's claim to her beloved horse.