Fiery Fiona

Summary
The official description of Fiery Fiona states: "Meet the beautiful and heroic Fiona — the mare with the glowing red mane — as she helps a young girl, Astrid Sundlo, discover that things aren’t always what they seem."

Astrid Sundlo
Astrid is the daughter of bakers and lives in Canter Downs, also known as Canter Hallow. She is fascinated with all horses, especially Fiona, although she has no horse of her own. On a trip to bring baked goods to her grandfather on Mount Whitemantle Astrid discovers a cave that was revealed after a recent mudslide. She finds a package containing old stonecutter's tools made of durium and finds a tassel mouse who she befriends and names Cork. She explores the cave, which she finds is actually a tunnel, and emerges in a previously unknown hollow near the Bella and Bello monument. She then finds a door with the legendary horses carved into it, but is unable to open it and goes to visit her grandfather instead. On her way back, she gets stuck in a storm and returns to the tunnel. While exploring, she meets Philenia True who summons Fiona to help bring Astrid home. Once home, Astrid discovers a Nix has invaded the family home. After putting out the fire it starts, she then takes Fiona to the forge where she finds out Fiona's durium horseshoe is bent. It can't be fixed without durium tools, which Astrid gifts Mr. Smithin, and a superheated fire. Just then the Nix reappears, starling Astrid. After he is chased away, Fiona's horseshoe is removed. Later, the Nix returns, and Astrid learns he only wants a warm fire to live in. She tries to return him home through the mysterious door, but is stopped by a mysterious Valkyrie. She then finds him a place in Mr. Smithin's forge. They repair Fiona's horseshoe, and Fiona leads Astrid and the Nix to Philenia's camp again where a burst of magic allows the Nix to return home. Fiona then bids Astrid farewell for a while, and finds a drawing of herself, Cork, Fiona, and the Nix from Philenia that she keeps as a memory of her adventures.

Fiona
Fiona is summoned by Philenia True and helps bring Astrid home. In the story, her durium horseshoe is bent. The Nix and Mr. Smithin help to repair her shoe.

Kaia Olav
Kaia is mentioned as being Astrid's neighbor. Not much else is known about her or her family

Mr. Smithin
Smithin lives and works in Canter Hallow. Astrid sometimes assists him at his smithy.

Mr. and Mrs. Sundlo
Astrid's parents run a bakery.

Nikolas Sundlo and Paal
Nikolas is Astrid's grandfather. His horse is Paal, and loyal Fjord. They both live in the Midwinter Mountains on Mount Whitemantle. Nikolas makes rustic furniture and hand-carved animal sculptures. He also lives in a cabin that he built himself. He is described as having wrinkled brown asking, and a crown of white hair.

Nix Darkling
The Nix Darkling invades the Sundlo home and leaves little footmarks on Tondy's bed, as well as setting the woodpile in the kitchen ablaze. The Nix then jumps from house to house, looking for a fire to live in, causing fires and ruckus wherever it goes. He eventually is given a home in Mr. Smithin's forge, but has no need for this as Astrid is able to return him home to the underground.

Philenia True
Philenia True is an old woman that Astrid meets after exploring the tunnel. She has set up a camp and campfire in the middle of the storm in the center of a circle of standing stones. She describes herself as a traveller, and her appearance is kind and welcoming, with brown, wrinkled skin and aquamarine eyes. She draws a picture of Fiona for Astrid which summons Fiona to them. She is most likely a seer, possibly even Fable herself, although this is never confirmed.

Tondy Sundlo
Tondy is Astrid's younger brother. He is fascinated by Nix Darklings.

Unnamed Valkyrie
An unnamed Valkyrie appears at the door to the underworld when Astrid attempts to return the Nix home. She is described as tall with black hair and wearing silver armor with a silver shield and silver-tipped spear. Nothing else is known about her. It is possible she is a ghost of a Valkyrie, similar to Sigga's spirit which guards the Rolandotter Vault.

Valto and Kumo Sundlo
Valto and Kumo are Astrid's elder brothers. They used to tease her when she was younger with scary stories of the Nix Darkling. Valto is described as tall, lanky, and fair. Kimo is described as short, stocky, and dark.

Various Horses
A number of unnamed horses are mentioned in this book, including a Root Pony, Mr. Vibbard's swaybacked dapple grey mare, Cloudskipper, a stratus horse (an unknown type of horse that is never mentioned again), and a luminescent green Dynasty horse (also a type of horse never mentioned again.)

There are also a number of named horses with no true description, including a mare named Sparkle who is referred to as a type of horse called a Glittermane, a massive Redwood Draft named Dax, a rainbow mare named Arca, and thousands of horse spirits that appear with the unnamed Valkyrie.

Various Magical Friends
A number of magical friends are mentioned in this story, including Cork the Tassel Mouse, Glow-Worms,