The ninth story of The Things They Carried is “Sweetheart of the Song Tra Bong.” The narrator explains that there are a lot of stories from Vietnam, but the best are the ones that rest between the improbable and bedlam. “Sweetheart of the Song Tra Bong” is a story he heard from Rat Kiley, who had a reputation for exaggeration, but who swore this story was true. It begins when Kiley was stationed as a medic at an aid station in the mountains west of Chu Lai, near the village Tra Bong. The compound overlooks the river, Song Tra Bong. Though the compound was not very secure, the soldiers enjoyed their duty there because there was little military discipline and no humping. The only soldiers that cared about fighting were a squad of six Green Berets, or "Greenies," who use the compound as a base for operations.

One day, the medics begin to idly discuss the idea of bringing a “mamasan” to the compound. They are quick to dismiss the idea, but Mark Fossie decides to pursue it. Six weeks later, his high school sweetheart, Mary Anne Bell, shows up wearing a pink sweater and culottes. The men all enjoy her company because Mary Anne is flirtatious, pretty, and curious. She gazes at the green mountains west of the camp, and she spends her time asking the men about mines and weapons. She eventually insists that Mark take her down to the nearby village and on the way back she swims in the river. One night, Mark Fossie wakes Rat to tell him that Mary Anne is gone. He thinks that she is sleeping with one of the other soldiers, but they search the bunks and find that she is not in the compound. She returns from an ambush with the Greenies. Angrily, he insists that Mary Anne not leave the camp and she agrees. However, her relationship with Mark Fossie now seems strained.

After several days, the medics wake up to find that both Mary Anne and the Greenies have left the compound, and they do not return for nearly three weeks. Rat explains that in a way she never entirely returned. When she does return to the compound, she ignores Mark and goes into the Greenie’s “hootch.” Mark sits outside of the hootch and eventually enters it with Rat and their NCO, Eddie Diamond, close behind. Inside, there is a strange smell, bones, and weird music. Mary Anne appears, wearing a blouse, a skirt, and a necklace of human tongues. She explains to Mark that he does not belong in this “place,” but she does not simply mean inside of the Green Berets’ hootch. She means that Mark does not belong in Vietnam. Mary Anne explains that when she is on patrol she feels alive in a way that cannot be felt anywhere else, and she then fades into the shadows. Rat and Eddie take the flabbergasted Fossie out of the hootch.

Rat explains that he can only speculate about what happened afterward, noting that the rest of the story is based on hearsay and not his own observations. He explains that Mary Anne continued to go out on the night patrols and that Fossie still loved her because no girl back home would ever understand Vietnam. Eventually, she would go out on patrols without the Greenies and the platoon would claim to sometimes—almost—catch sight of her in her pink sweater and her necklace of human tongues, “ready for the kill.”