Retrieval of Ilia's Memory
The Retrieval of Ilia's Memory is a particular task in Twilight Princess that operates due to the aftermath of the Ordon child abductions by King Bulblin and his troupe. After the children quickly quarantine themselves from their pursuers inside Renado's house in Kakariko Village, Ilia, the eldest, is reported to have taken shelter in Telma's Bar, a pub within the confines of Hyrule Castle Town. When Link finally finds her after visiting with the other children in Kakariko Village, he realizes she now suffers from severe memory loss as a product of her abduction. The events of this quest take place after completing the Temple of Time and having found the third Mirror Shard.
This quest is tied to the restoration of the Dominion Rod's powers.
Upon approaching Hyrule Castle, Link receives a letter from Renado, who asks him to return to Kakariko Village. Once there, Renado explains that Telma's friend Shad has been researching the heavens and is currently in the basement of the sanctuary. He states that when Ilia was saved, she overheard someone talking about the rod of the heavens and it would be useful to work their way backward from the very place Ilia first lost her memory, implying that Telma may know something. Renado then gives Link a letter to give to Telma, detailing how to treat Ilia to get her memory back.
Link then heads to Telma's Bar. Handing over the letter, Telma mentions that is was the town doctor, Borville, who first brought Ilia to her pub. Aware of Borville's uncooperative nature, Telma gives Link the Invoice, which illustrates the money owed to her by Borville. Link then heads to the medical clinic located on the East Road of Castle Town. Inside, after showing Borville the Invoice, he mentions a carving that was once in Ilia's possession; he tells that he had spilled medicine over the statue, which made it "stink awfully", prompting him to place it outside to dry. Unfortunately, it was stolen. Borville then proceeds to go back to work. Exploring the clinic, Link uncovers the Medicine Scent by pushing aside a crate. Inside, Link is then able to transform into a wolf in order to learn the new scent. It guides back to Louise, Telma's cat, who informs Link that she stole it but was attacked by a pack of Stalhounds, who took the statue and can be found at the southern gate, but only at nighttime.
After Link defeats the Stalhounds and acquires the Wooden Statue, he heads back to Kakariko Village. Upon receiving the statue, Ilia recovers "part" of her memory. Gor Coron, who began to accompany Renado some time ago, recognizes the statue as that of an ancient tribe that protected the Hylian Royal Family. He marks the location of the village on Link's map and asks Darbus to unveil the entrance that was covered by a rock-slide. Before entering, Darbus warns Link that the village is infested with enemies. In order to proceed, Link must defeat 20 Bulblins. After the battle, an old woman exits her house at the far end of the village. She introduces herself as Impaz, the only remaining resident of the Hidden Village and a descendant of the Sheikahs. She recognizes Link from Ilia's tales and proceeds to give him Ilia's Charm. Link receives this item, then goes back to Kakariko Village and shows the object to Ilia. After a short sequence, Ilia regains her full memory and gives back the Horse Call as a reward (interestingly, Link was going to receive this item the day he was going to deliver the Ordon Sword in Hyrule Castle Town; in fact this is the item Ilia was making the day she asked her father, Bo, to allow everybody except Link to meet her inside her house, as the Horse Call was intended to be a surprise gift for him).
Although optional, Link can talk to Telma to let her know that Ilia has recovered her memory.
Before Link receives the message from Renado to begin this quest, he and Midna learn from Ooccoo that the Dominion Rod lost its power; fortunately, when Ilia recovers her memory, she tells Link that Impaz was waiting for a messenger who would have the rod of the heavens; indeed, Link shows the rod to Impaz and she gives him a book that holds the clues on how to give back the rod its power, as well as how to reach the City in the Sky. The game resumes the main quest from this point.
Despite the importance of this quest to the game's plot, it is possible to finish the game without fully recovering Ilia's memory. All Link needs to do is not show the Ilia's Charm to Ilia; the main quest can be continued by showing Impaz the Dominion Rod on the first visit to Hidden Village to obtain the Ancient Sky Book and immediately embarking on that part of the adventure. Nothing is permanently missable in this way; Link can go back and complete this part of the quest at any time. There is no alternate ending attainable by not completing this objective; the same credits sequence plays at the end regardless of whether Link fully restores Ilia's memory or not.