January 30–31, 1968. The Tet Offensive begins. Trapped at a firebase, Cherry comforts a fellow Red Cross “doughnut dolly” and bonds with the two soldiers defending their bunker. McMurphy and K.C. are locked down in the I Corps Headquarters, where McMurphy learns K.C. has been skin-popping heroin and helps her through withdrawal. Beckett visits Mai at her family’s hamlet and is attacked and held captive by Mai’s brother Tran, a Viet Cong soldier. Dr. Richard and a still-recuperating Dodger defend the barricaded hospital, but Dodger unnerves the doctor by estimating the distance of falling shells. Wayloo Marie tries to capture the combat around the base, following Boonie and other soldiers around China Beach. As morning breaks, Boonie clears the hospital barricade to reach Dr. Richard and Dodger. Beckett is released and protects Mai’s hamlet by talking down ARVN soldiers who enter her home. Cherry survives the night at the firebase, but is killed by an explosion as she exits the bunker the next morning.

In 1967, Dr. Richard confirms K.C. is pregnant and several months along. Boonie asks K.C. if she thinks Mac is the father, but she declines to answer him. She greets Mac with the news of her pregnancy when he returns to China Beach and Mac asks her to come to the Philippines with him, but pours cold water on the idea of her running a store or business if she does. Boonie continues to help K.C., developing a rivalry with Mac after K.C. has a fainting spell. He urges her not to follow Mac and promises to always take care of K.C. and her baby. Mac is severely wounded when he is hit in the groin and abdomen by enemy fire while in a helicopter. K.C. still intends to travel with Mac on his evac flight and argues with Boonie over her future. The two share a passionate goodbye, but K.C. decides not to leave and sends Mac off. Warned by Richard she won’t be able to travel much longer without risk of premature birth and loss of the baby, she tells him that she had her first experiences with the baby moving, which has changed her perspective on her future.

In 1967, McMurphy bonds with Dodger, treats an injured Vietnamese girl with the help of Dodger and his gorilla suit, and deals with most of the base mistakenly believing it is her birthday. She tries to resist Boonie and Dodger giving her a birthday “baptism” by ocean but ends up frolicking in the water with them. That night, she surprises her friends at her birthday celebration with the gorilla costume before they serenade her with Happy Birthday to You.

In October 1969, Frankie attends the funeral of a Black revolutionary, contrasted with McMurphy’s experience witnessing the funeral of a Marine Corps veteran after her father’s burial in Season 2’s “The World.” Now living in Chicago after her discharge from the Army, Frankie tries her hand at stand-up comedy with little to show for it. She draws the attention of two Black Panther revolutionaries and Vietnam veterans, Eddie (guest star Scott Lawrence) and Rashid (guest star Basil Wallace), who invite her to a party. She grows close to Eddie, who advocates for a nonviolent approach for change; however, she is disgusted by Rashid’s cache of weapons and his support for the Viet Cong and violent revolt in the U.S. Eddie asks her to attend the trial of Bobby Seale and support the protests for the Chicago Seven. She is horrified by the treatment of Seale in the courtroom, but refuses to support Eddie and Rashid in protesting it. Later, Rashid informs Frankie that Eddie was killed in his bed during a police raid. She attends Eddie’s funeral, witnessing as Rashid is dragged away by police when he lights an American flag on fire. At her stand-up set, Frankie struggles through her normal routine before giving an impassioned monologue on her status as an African-American Vietnam veteran.

In late 1969, McMurphy auditions for Lila’s production of My Fair Lady, which stars Dr. Richard as the male lead. However, she is beaten out for the role by Gloria Dawn. Sarge Pepper approaches McMurphy with opinions on how to ask Lila to marry him. McMurphy visits Richard in his tent, where they share a drink to each having less than 100 days left in Vietnam. McMurphy tells him she doesn’t want to miss him when their tour is over, but they are interrupted by Gloria Dawn. Walking back to the base, she comes across the newly engaged Lila and Sarge Pepper, who plan a quick wedding to avoid military scrutiny. After the My Fair Lady performance, McMurphy tells off Richard, who believes she is still upset at not getting the part, and informs him she’s tired of no one knowing her true self. He wins her back with a performance of “On the Street Where You Live” and admits to her that he feared losing her as a friend if he pursued her romantically. The pair finally admit their love for one another and kiss, then decide to get married the next day after Lila and Sarge Pepper. The next morning, Richard receives a shocking message: His ex-wife has been critically injured in a car accident and he must return home, prematurely ending his tour in Vietnam and shelving his plan to marry McMurphy. The two attend Lila and Sarge Pepper’s wedding in the church ruins. Prior to boarding the helicopter out, Richard invites McMurphy to join him in Boston once her tour is over, but she declines. As his helicopter departs, Richard begins to sing “I've Grown Accustomed to Her Face,” as does McMurphy in the hospital ward.

On April 25, 1975, five days before the Fall of Saigon, K.C. — now living in Bangkok and operating a nightclub with the same name — is contacted by Trieu Au, seeking help getting eight-year-old Karen out of the country. K.C. returns to Vietnam, finding Trieu Au and Karen living in a decrepit apartment in a Saigon alley. Trieu Au, critical over K.C.’s avoidance of her and Karen for the past six years, asks for help getting Karen out of the country, worried that the city’s citizen committees will round them both up when Saigon is taken by the approaching North Vietnamese army. Intending to take them back to Bangkok, K.C. brings the two to the American embassy, where she is forced by the clerk to pay a hefty bribe for Trieu Au’s passage out of the country. However, Trieu Au is violently questioned by a citizen patrol and kidnapped. At the embassy the next day, K.C. is told her local hospital records from Karen’s birth aren’t enough to prove U.S. citizenship, requiring her to seek out a forger in Saigon to purchase them. Upon returning to the apartment, they find locals have cleaned the entire place out in their absence and K.C. finally tells a devastated Karen that she is her birth mother. The two return to the American embassy, where they wait all day and night to reach the helicopters ferrying civilians from the roof. Hoping to soothe Karen, K.C. promises to buy Karen a canopy bed while they wait. Finally reaching the roof, the two are refused entry to a helicopter, but K.C. begs a Marine to take Karen. She writes Boonie’s name on her dress in lipstick, then watches as the helicopter departs.

Elsewhere in Vietnam, Dodger — still working as a government contractor — finds himself at the abandoned China Beach facility, on the run from approaching North Vietnamese troops. Entering the old hospital ward, he finds the Kansas flag once hanging in the ward, triggering memories of his time in China Beach. He discovers an apparent South Vietnamese soldier living in the ward and begins digging his own grave, convinced he will die at China Beach once the North Vietnamese soldiers arrive. He discovers the apparent soldier living in the ward is a woman when two North Vietnamese soldiers try to rape her; he kills both. Dodger tells the woman to leave the base when the North Vietnamese regulars arrive, intending to make a final stand, but she convinces him to escape with him.

In 1969, K.C. discovers McMurphy lounging in her Bangkok apartment, four months after K.C.’s departure from China Beach. On R&R before her tour’s impending end, McMurphy is joined by a smitten soldier, Maltby, who tells K.C. they’ve spent most of their trip drinking heavily. On their way out, the group is interrupted by Trieu Au returning with a two-year-old Karen, shocking McMurphy. At the bar she operates, K.C. is approached by Tucker, an old manager who wants to go into business with her — and bed her. He brings K.C. and McMurphy to the future site of her nightclub, where McMurphy questions the wisdom of K.C. raising her daughter and operating a nightclub in Bangkok — a sentiment shared by Trieu Au. McMurphy passes out before finishing a toast to the future and wakes K.C. with her vomiting the next morning. McMurphy confronts K.C. about leaving without saying goodbye, but K.C. snaps back that the rest of their friends at China Beach have moved on and she needs to as well. McMurphy reveals to K.C. that she fears returning to China Beach because her tour is about to end; unlike their friends, all trying to move on in the U.S., she does not want to. A resigned K.C. informs McMurphy that Trieu Au has taken Karen back to Vietnam and expresses an unwillingness to return for her or get involved in her life. Before she departs, McMurphy tells K.C. she intends to stop heavily drinking, while K.C. hopes to grow her nightclub and business interests. Struggling to find the right goodbye, the two happily recall the cheerleading sets they performed together on the first night of the Tet Offensive.

In February 1988, the veterans of China Beach attend a reunion in Youngstown, Ohio. The party attended by Boonie, Linda, and Karen, who conducts interviews during the reunion; McMurphy, Joe, and their two-year-old daughter Maggie; Beckett and his teenage son Malcolm; Dodger and Archie; Lila and Sarge Pepper; Frankie; Wayloo Marie, now a famous daytime talk show host; and Dr. Richard and Colleen, who tells Karen in an interview that she suspects Richard of having an affair with his receptionist. Karen is disappointed when K.C. skips the reunion, despite being invited by McMurphy. During her interview with Karen, McMurphy recalls her final day in Vietnam in late 1969, when she gathered sand from the beach and where Dr. Singer and Gloria Dawn threw her a going home costume party. The party was interrupted when a tank crashed through the front of the hospital ward. She bonds with an injured soldier nicknamed Lurch (guest star Neal McDonough), whom the medical staff determine will quickly bleed out and die once the pneumatic pants he is wearing are removed. Richard discusses his love for McMurphy and how his career feels insignificant compared to the time he saved lives in Vietnam, reminiscing to a moment when he, Beckett, and McMurphy buried unidentified body parts in a ceremony on the beach (first seen in “Juice”). Wayloo Marie says she is grateful for her experience, as it changed her for the better. Dodger, still in love with McMurphy, recalls her departure from his hometown in 1977 and joins Frankie on-stage to sing “When a Man Loves a Woman.” Sarge Pepper compares his experience in World War II among educated and well-off enlisted men to his time in Vietnam, spent entirely alongside drafted soldiers from poor and destitute backgrounds. Lila, who talks about the strength of their marriage, reveals Sarge Pepper has terminal lung cancer. Dodger and Boonie are interviewed together, but Dodger inadvertently insults Boonie when he makes light of Boonie’s accident and his belief that there were no heroes in Vietnam. Later, he tells Boonie and McMurphy that he feared attending the reunion, worried it would stir up bad memories, but he understands now that those memories — and his friends — are always present and will always be a part of him.