A series of eight short books by Mary Stanton. They're about unicorns. Of Balinor.
On a more helpful point, it's a surprisingly inventive, fantasy-steeped horse story. The series begins with the heroine Arianna (Ari for short) waking up in a hospital with both her legs broken from a horrific accident, only recalling her own name—and that of her horse, Chase. After encountering her collie Lincoln, who came with a ruby necklace, she is discharged to Glacier Ridge Farm with her foster parents and the local Dr. Bohnes, who makes sure her legs mend properly. Eventually she starts hearing a voice in her head whenever Chase is angry, having strange dreams where a unicorn mare talks to her, and finding spiral-shaped pebbles around the stable.
When her foster parents decide that they need to lease Chase out to Lori, a wealthy and snobby girl who's taken a shine to him, both Ari and Chase are adamantly against it despite Ari knowing that the hefty hospital bills leave them no other choice. One spectacularly bad session with an angry Chase later, the pair decide to run away to the nearby caves—and they're unfortunately followed by Lori, who won't give up until she gets Chase.
After falling through a tunnel into a strange forest, they get through it unscathed and end up in a town called Balinor. It's discovered that the animals can talk, but ever since their princess and her unicorn went missing, they have slowly begun losing their speech. Turns out that Ari is the Royal Princess, while Chase is both a unicorn and the Lord of the Animals. His horn was broken when the royal family got betrayed by the malevolent Shifter.
Both the necklace and the stones Ari found were actually parts of Chase's horn, which she eventually restores, but that's nowhere near the end of their troubles: They still have to defeat the Shifter. When that's done, Ari needs to earn the right to continue as the Royal Princess through three trials that test her leadership and diplomatic skills—and even when both of those tasks are done, the latest book ends when she begins the search for her parents and brothers.
This series contains examples of:
- A Girl And Her X: Unicorn, in this case. Arianna and Chase are bonded by magic and the narrative spends a not insignificant amount of time hammering home that Chase is hers.
- Author Appeal: Aside from Mary Stanton's genuine horse knowledge, which isn't surprising as she owns several of them, she spends an awful lot of time describing Chase and how SUPER-SPECIAL-AWESOME he is. It's obviously platonic, though, and not exactly unusual for the genre.
- Bond Creatures: Every Royal Princess is Bonded to the (current) Lord of the Animals to ensure that the creatures of their world can talk. When Ari and Chase were wounded amnesiacs recuperating in our world, it wasn't a good thing, but they recover.
- Capital Letters Are Magic: The Gap, Entia the Shifter, the Shadow Unicorns, the Celestial Valley... this happens a lot.
- Carbuncle Creature: All of the Celestial Valley and Royal Unicorns (Atalanta and Sunchaser respectively, for example) are this, having gemstones at the base of their horns.
- Carnivore Confusion: Surprisingly averted. See Veganopia below.
- Cool Old Lady: Eliane Bohnes, a doctor and Resistance member who- even as everyone around her is losing their minds- responds to the Shifter's takeover with only mild frustration.
- Cool Unicorn: Many. Especially Chase, who's pictured above.
- Deadly Race: Ari and Chase enter in a steeplechase with five-foot tall burning fences.
- Defanged Horrors: Kraken and the Shifter. Obviously they were meant to be scary, but Mary Stanton's writing abilities and her use of less-than-pleasant smells or sounds makes her villains rather jarring.
- Heroes Want Redheads: Finn, who starts out asking Arianna far too many uncomfortable questions about herself and her unicorn, ends up being liked by both girls.
- In a sort-of version of this trope, Finn often ends up working with Rednal, a red celestial unicorn.
- Humanity Is Superior: While Entia likes the power of other forms, he really likes humans... especially their hands.
- The Magic Almost Goes Away: The animals of Balinor were starting to lose their speech by the time Ari and Chase got back.
- Magic Pool: The Celestial unicorn Atalanta uses one to keep track of things in Balinor.
- The Masquerade: Inverted in the beginning—neither Ari nor Chase remembered who they were, and thus the masquerade was imposed upon them by others to ensure their safe recovery and to make sure the Shifter wouldn't find them. Played straight several times later, when using their real identities would be risky.
- Modest Royalty: Used dead straight with Arianna, though Chase seems to have no problem lording over people when they disrespect his mistress.
- Orphaned Series: Apparently. The last book is the eighth, released in 2000. Stanton last posted on her Facebook page in 2013, referencing wanting to write a conclusion and wrap up the last few plot ends, but nothing has since materialized.
- Eerie Pale-Skinned Brunette: Lady Kylie.
- Physical God: The animals of Balinor treat the Celestial Valley unicorns, specifically Atalanta, as this.
- Portal Network: The Gap, which is not to be confused with the trendy clothes store chain.
- Royals Who Actually Do Something: Ari needs to do a LOT to get Balinor back in order: Fix Chase's horn, defeat the Shifter, get the palace up and running, find out which of the nobility is still loyal/alive...
- Rule of Three: Ari does three tests to restore the sceptre to its true power, undergoes three trials in By Fire, By Moonlight, and she has two older brothers which makes her the youngest of three.
- Scaled Up: Lady Kylie has this ability, in part to show just how eeeeevil she is.
- Snakes Are Sinister: Lady Kylie in her snake form
- Sssssnake Talk: Servants of the Shifter, like Lady Kylie, do this regularly.
- Talking Appliance Sidekick: The royal sceptre, which at first can only speak if you ask it a question, but later gains the ability to talk on its own.
- Unicorn: Well, yeah.
- Veganopia: Everyone is vegetarian since the animals of Balinor can talk. Probably helps that Balinor has magic to prevent vitamin deficiencies. Yet it is also mentioned the only meat the carnivores are allowed to eat are fish and bugs.
- Voluntary Shapeshifting: Entia, the Shifter.
- You All Meet in an Inn: While it doesn't start there, the first place Ari finds in Balinor is in fact an inn, and later uses it as her primary base of operations.