Hwin is a talking horse of Narnia who was captured at a young age and taken to Calormen to be a slave. While there, she pretended to be a dumb animal in order to go unnoticed. She became the chief horse of the Lady Aravis and served her well. One day when Aravis rides Hwin to a secluded place, Hwin is forced to speak up and reveal her true nature in order to prevent Aravis from committing suicide. She tells Aravis not to waste her life by death but instead to escape with her to Narnia, where they can both be free.
Aravis is glad to take this option, and they both contrive an elaborate plan to get them out of the country secretly. But while on the run to Tashbaan, their plan is nearly ruined when they are forced to join up with a strange boy and his steed. They soon discover that the other pair is also trying to escape to Narnia, and they decide to travel with their new friends Shasta and Bree.
When they reach the Calormen city of Tashbaan, itís Hwinís idea to make themselves look tired and dirty so that there would be less chance of them being noticed as they travel through the city. On their way through Tashbaan, Shasta is mistaken for someone else and separated from the rest of the group. Aravis is then recognized by an old friend of hers, Lasaraleen. With her help, they find a way to escape Tashbaan.
When the group meets up again at the Ancient Tombs, where all four had agreed to meet if anything went wrong, they continue their journey North to warn King Lune about the planned attack by the Calormenes on Archenland.
On their way to warn the king at Anvard, they are ambushed by a Lion. Aravis is wounded and Hwin rushes her to a Hermit's dwelling, where the find safety. Aravis, Bree and Hwin stay with the Hermit, while Shasta runs on foot to warn the King.
Aslan appears to them later and though Hwin is frightened, she finds the courage to approach Him. Aslan welcomes her and says that joy will be hers. Later, Shasta, who is revealed to be the long-lost Prince Cor of Archenland, arrives and invites them to Anvard, his new home. Hwin and Bree later leave Anvard to return to Narnia. Hwin married and lived happily to a great age in Narnia, and is numbered among those at the Great Reunion.