Sagi Christopher Gaze the red panda and Azul Steve Marvel the Indian peacock inhabit a sun-soaked tropical island in the South Seas. One day they discover a little girl washed ashore after a storm, and they decide to take her in. A chest with her belongings bears the letters "R-O" on its broken nameplate; the animals name the girl Ro, Kelly Sheridan, and she grows up playing with them and an Asian elephant named Tika Susan Roman, though she has lost most of her past except for a lullaby from her birth.
Ten years pass, and Antonio Alessandro Juliani of Apollonia sails the South Seas and lands on Ro's Island. Ro, now a young woman who can talk to animals, saves him from a crocodile surge. Antonio invites her to Apollonia to help uncover her history, and Ro agrees, bringing along three friends. On the journey, Ro and Antonio begin to fall in love.
In Apollonia, King Peter Russell Roberts and Queen Danielle Patricia Drake are stunned by Ro's arrival. While Antonio has been away, Peter arranged a marriage to curb his restlessness. Peter immediately dislikes Ro for disturbing his plans, but Antonio’s sisters Rita Britt McKillip, Sofia Chantal Strand, and Gina Carly McKillip, along with Danielle’s pet rhesus monkey Tallulah Bets Malone, befriend Ro and her animal companions. With Ro homesick, the trio and the animals move into the royal greenhouse to feel more at home.
The plot thickens when Antonio’s betrothed, Princess Luciana Candice Nicole, arrives with her mother Ariana, so Antonio can meet them. Ariana is secretly the daughter of nobles whom Peter demoted to swineherds after treason. Ariana had abroad, married an elderly king to become queen, and has now returned to enact revenge. Sensing Ro as a threat, Ariana sabotages Ro’s attempts to fit in, though Antonio only falls deeper for Ro and Luciana grows sympathetic toward her.
Becoming discouraged, Ro contemplates returning to her island. The animals rally around her, helping her dress for the royal engagement ball. At the ball, Ro’s beauty and grace impress everyone, and Antonio privately proposes. Ro declines, unwilling to defy Peter. Outside, Sagi spots a carriage bearing the same flag Ro once saw, and the horse reveals it belongs to Paladia, a distant kingdom where people have three sons and no daughters.
A confrontation ensues as Peter and Antonio argue; Antonio abdicates the throne to Rita and leaves a note for Ro, planning to run away with her. Tika overhears and hides the note, fearing Ro’s loss. Ariana sends her pet rats to spread “sunset herb” through the kingdom, causing many animals—including Tallulah and Azul—to fall into a coma. Peter imprisons Ro and her friends, convinced they brought a disease to Apollonia.
Peter strikes a deal: Ro and the animals can go free if Antonio marries Luciana. Antonio reluctantly agrees and Ro and the animals are sent away on a ship. Tika apologizes for hiding the note, and Ro forgives her. A sailor in Ariana’s pay dumps them overboard, but they are rescued by dolphins. Ro experiences a childhood memory flash on the return to life, revealing her full name: Rosella.
Back in Apollonia, Ro learns from a small bird that Ariana laced the wedding cake with sunset herb to kill Peter and Antonio. She makes an antidote to wake Azul and the others but is blocked by guards. Tika interrupts the wedding and brings Antonio to Ro’s side, while Sagi carries the antidote to Tallulah, reviving the others. When Ro accuses Ariana, no one believes her—until Luciana confesses that her mother warned against eating the cake, calling it bad luck. Ariana tries to flee in a carriage, but the vehicle crashes into a pigsty.
Antonio finally proposes to Ro, who is warmly welcomed into the family. When Ro reveals her full name, Queen Marissa of Paladia Kate Fisher steps forward and explains that her daughter, Princess Rosella, was lost in a shipwreck many years ago. Ro’s memory returns, confirming she is the long-lost Paladian princess. Ro and Marissa sing the lullaby from Ro’s childhood, establishing their kinship. Ro and Antonio marry, and Luciana meets a handsome prince at the reception. Ro and Antonio then set off on new adventures, with Ro’s faithful companions—Tika, Sagi, Azul, and Tallulah—along for the journey.
