In the arena of the 75th Hunger Games, while diving for seafood, Peeta Mellark found a pearl inside an oyster. He gave it to Katniss Everdeen as a gift and promises that he will protect her. Although a small token, the pearl was a clear message of love from Peeta, and Katniss knew it; she kept it close by her and constantly protected it, as Peeta had vowed to protect her. While residing in District 13 following her rescue from the arena, Katniss kept it in the drawer that held her clothing and few possessions.
When he found it, he told Finnick Odair that when enough pressure is placed on coal it will turn into pearls. This is an inside joke between him and Katniss referring to Effie Trinket's mistaken pronouncement before their last Hunger Games, who confused pearl creation with the creation of diamonds.Katniss closely guards his gift, thinking that it's the only gift she can truly accept. She knows that her mother and Prim will surely know to return the pearl to Peeta if she dies protecting him, which she's positive she will.
She later brings it to District 13, waking up in the middle of the night and looking at it. She keeps it with the spile and the other items she received in the arena, like Peeta's locket. She then takes it to her mission to assassinate Snow with Squad 451. Throughout Mockingjay, Katniss closely guards the pearl, keeping it in a silver parachute in a dresser drawer. Just before the bombing of 13, Gale goes back to Katniss' room and retrieves it, along with her hunting jacket, her mother's wedding photo, the plant book, and the contents of her dresser drawer. Later, Katniss' mockingjay uniform has a pocket in which Katniss stores her pearl throughout the Battle of the Capitol. The last time the pearl was mentioned was when Katniss drops the keys to unlock Peeta's handcuffs in her pocket and she hears them clinking together. After that, the pearl (along with the spile and the mockingjay pin) is returned to Katniss and is in her house in the Victors' Village.
- The Hunger Games, Chapter 6