Originally the 5th book… The Horse And His Boy is now the 3rd in the series. Based in the year 1940 in normal human year count, we meet Shasta and find out a little bit about his life. A Tarkaan arives with the horse Bree and Shasta hears the Tarkaan bargaining with his father for the purchase of him as a slave. At this Shasta decides to run away with the Tarkaans horse, Bree. While continuing thier escape, Shasta and Bree get chased by a lion and end up running next to Aravis and Hwin who are also being chased by a lion. After running from the lions, it is discovered that they are all escaping to Narnia and decide to escape together. Bree, Shasta, Hwin, and Aravis share the stories about why they are escaping. As they continue towards Tashbaan they start making plans as to how they are going to get through Tashbaan without drawing attention to themselves. While riding through the streets of Tashbaan, the Narnians mistake Shasta for Prince Corin. While with them in the Palace of the Tisroc, Shasta hears King Edmund reveal something that is worrying him. After the King has revealed his thoughts, the Narnians make plans to leave Tashbaan and head back to Narnia. When the real Corin turns up, Shasta explains what is going on then leaves to find Aravis and the Horses. After Shasta has left the Palace, he makes his way to the Tombs outside Tashbaan and finds Aravis and the horses are not there yet. He was getting himself ready for a second night in the tombs when he see’s Bree and Hwin with someone who is not Aravis. Soon after the Narnians left with Shasta, Aravis got caught up with an oldaquaintence of hers who agrees to hide her and help her escape the city. During the escape, Aravis and Lasaraleen get trapped in a room with the Tisroc. While trapped in the room, the Girls over hear Prince Rabadash’s plans to Capture Archenland and the Enter Narnia and Capture the Queen Susan, and how the Plans also include a way out for the Tisroc if Rabadash’s plans fail. After the small secret council has left the room, Aravis finally manages her escape from Tashbaan and meets up with Shasta, Bree, and Hwin at the Tombs. After they finally make it across the desert, they decide it is time for a much needed rest. When they awake, the realise that they have rested longer than intended and head off towards Archenland. They were traveling at a steady pace until they saw that Rabadash’s army had entered the Valley, after that they ran as hard as they could. They reached the Hermit of the Southern March when almost out of energy, and Shasta was told that if he kept running on foot, he could make it to King Lune in time to Warn him of the Danger. Shasta made it to King Lune in time to warn him of the coming danger. On his way to Anvard after King Lune, Shasta got lost. He was telling himself he must have been the most unlucky person when he met Aslan who then explained some things to him. Shasta was trying to alert the Narnians of what was happening in Archenland when he was found by 3 dwarf brothers who fed him and then let him have a much needed sleep. After he woke, he met King Edmund, Queen Lucy, and Prince Corin and ended up joining the Narnian Army. Shasta rode with the Narnian army and joined in the Battle at Anvard. Mean while, the Hermit and Shasta’s friends watched from the Hermits Magical pool. After the battle, there was surprise in store for Shasta. Aravis, Hwin, and Bree were discussing their plans to continue into Narnia when they received a visit from Shasta who tells them of the Story of how he ended up living the First part of his life in Calormen. While at lunch, and discussing the matter of the prince Rabadash and what his punishment shall be. The Lords and Ladies recieve a visit from Aslan who gives Rabadash a most fitting punishment of his own. Afterwards things turn back to normal in Narnia and here ends another Story from the Magical Land of Narnia.
Summary from Narniafans.com