The episode starts off on Sun working in her garden and looking quite elated. In a scene very reminiscent of her kidnapping in "The Long Con," Sun hears the bushes behind her rattle, but is relieved to see that is Jack, who has come to check up on her pregnancy. Sun seems reluctant to answer Jack's questions, regarding basic things such as morning sickness and bleeding, but he explains that "now that [he's] back, [he] just wanted to make sure that she was doing okay." Sun says she is fine and Jack leaves.
Flashback: A recently married couple, Jin and Sun are talking on their cellphones. They seem very happy, much like their relationship currently, and are discussing their new apartment. After explaining that he has nothing but the bed set up, Jin tells Sun that he must get back to the office. But Sun manages to tell Jin that she loves him "madly" before she hangs up. As she sits down on a park bench, a middle-aged woman with a newspaper comes and sits down next to her. "Is this you?" the woman asks, pointing to the paper. The camera focuses on the picture and we see that it is one of Jin and Sun on their wedding day. Sun confirms that it is her and the woman compliments Sun on how lucky she is to have married such a handsome man. Although she seems innocent, the woman knows much about Sun and her family. "Your father is Mr. Paik? Of Paik Automotive?" she asks, "Very powerful family." A startled Sun asks the woman who she is, but the woman disregards the question and says that it would bring much shame to the Paik family to know that Mr. Paik's daughter married the son of a fisherman. Sun, however, says that she knows this "and it doesn't matter." Nevertheless, the woman continues. She asks if Sun also knew that Jin's mother was a prostitute. "I will be back here in three days. At five p.m.," the woman says, "You will bring me one hundred thousand dollars." "If you love your husband as 'madly' as you say," she continues, "you will spare him the shame of learning the truth." The woman leaves as Sun sits in fear and shock on the park bench.
The story moves its focus back to Desmond, Charlie, Jin, and Hurley who are in a desperate attempt to figure out the identity of the parachutist. Desmond, however, although she recognized him, says that he has "never seen her before in [his] life." As the parachutist awakens, she starts to mumble things in different languages. Luckily, one of these languages happens to be Spanish and Hurley translates her ramblings as "I'm dying." And she's right because Desmond soon discovers a branch that has pierced the parachutist's side. Hurley starts to panic, but Desmond orders him to go look in the parachutist's pack for medical supplies. Desmond volunteers to run back to the beach to get Jack, but Charlie retorts with the fact that it isn't safe because they're in the middle of the jungle and there are people on the island who want the survivors killed. Desmond, however, does not agree and fires back with, "Nobody knows we're here!" But, in pure coincidence, Hurley pulls a flare gun out of the parachutist's pack and accidentally fires it off. "Oops," says Hurley.
Flashback: Jin and Sun are inside their new apartment and Sun is looking through the boxes of photos. She begins to ask why Jin doesn't have any pictures of himself or his family, but Jin says that his family didn't have a camera when he was growing up. Sun seems surprised by this and continues to ask Jin about it. Jin, however, becomes very defensive and starts, it seems, to make up a cover story about why he does not have any pictures. Sun can tell that he is lying because he is ashamed of his parents, but she drops the subject lest she embarrass and anger him further.
Back on the beach, Sun is helping Kate with her tent while she questions Kate about what she thinks happened to Jack while he was with the Others. Sun claims that he has been acting different since he's been back. "He says that he was pretty much a prisoner and the only reason why he cooperated was 'cause he thought they'd let him off the island," Kate tells her. Sun is still not so sure and she continues to tell Kate that Jack might be working with the Others to get to her baby because he came to her earlier and was asking about her pregnancy. Unfortunately, the only think Kate can do to sway Sun from her opinion is tell her the truth--that Juliet told Jack and her that the Others take the babies for research. Sun confronts Juliet about this information and Juliet tells her very bluntly that all the pregnant women on the island have died. Sun is in shock.
Jin, Hurley, Charlie, and Desmond are still having trouble communicating with the new island inhabitant and what to do to save her. Just in the nick of time, however, Mikhail, who we were previously led to believe had been killed by Locke and the 'sonic fence,' appears out of the jungle. Mikhail turns and runs as fast he can, but Jin, a trained hitman, chases after him. Using his knowledge of martial arts and fighting, Jin successfully takes down Mikhail and gets him in a headlock. "Who are you!?" Desmond asks Mikhail, pointing a flare gun at Mikhail's chest and threatening to shoot. "As your friend pointed out," Mikhail responds, "I've already died once this week." Mikhail tells them that he understands the parachutist and can and will save her life if Desmond lets him "walk away as if [he] never came upon you."
Flashback: Sun has found Jin's father and he recognizes that she must be Sun. They go inside to have some tea. During their conversation, Jin's father reveals that Jin's mother "was with many men" and that she left him with the baby to raise on his own, not knowing if it was even his child--"But who else would take care of him?" he asks. This very much parallels Sun's situation on the island because Sun has been with many men and is not sure if the baby is Jin's. Mr. Kwon then proceeds to tell Sun that she can never let Jin know that she met his father "or that his mother is still alive." "Do not make him suffer this shame," he says.
As Sun is sleeping, Juliet walks in to her tent and tells Sun that, if she wants her to help her and her baby, she must come with her. Sun, obviously, is reluctant and suspicious of Juliet's intentions, but Juliet tells her that she may still have hope. As they arrive at the Staff, Juliet tells Sun that she is going to look at the fetus and determine the D.O.C., the date of conception--hence the episode's title. Juliet continues, "If you, [Sun], got pregnant off the island, then you and your baby will, probably, be okay."
Flashback: At Paik Automotive headquarters, Sun confronts her father to ask him a favor. "I... I need one hundred thousand dollars," she says. When he asks her why she needs this money, Sun stands up for herself and tells him that she has pretended to not know what he does long enough. "I've allowed you to keep your control over me," she continues, "I will continue pretending as long as you give me the money I am asking for. No questions asked." He agrees, very reluctantly, that he will give her the money under one condition--if the money is for Jin, it is he who will bear the debt. "He will no longer be a floor manager. He will be working for me," says Mr. Paik thus revealing that Sun led to Jin becoming a hit-man.
Back with the parachutist, Mikhail attempts to save her life, but Hurley accidentally slips out that she had a satellite phone. Mikhail successfully pulls out the stick and removes the blood from the lung and surrounding area.
In the Staff, Sun asks Juliet why she is helping her. Juliet tells her that she once told women that they were pregnant and that she loved seeing their faces light up with happiness. "Then I came here," she says. Now, she only gives bad news to her patients and she has lost nine of them in the three years she's been on the island. "I'm helping you because I want to tell you that you and your husband got pregnant before you came here," Juliet concludes, "I'm helping you because I want to give good news again." They walk down the hall and enter the locker room where Kate had found the fake beard and theatrical glue in the season 2 episode, "Maternity Leave." Kate, unfortunately, missed the locker with the secret lever that opens a storage room behind the lockers when she was there. "Why is this room hidden?" asks Sun. Juliet answers, "It's where we brought the women to die."
After Mikhail confirms that Naomi will be fine in a day and a half, due to the island's healing properties, Desmond lets him leave, much to Charlie's dismay. But soon after Mikhail leaves, Jin notices that the satphone has been taken. Jin, once again, chases after Mikhail because he believes that Mikhail took the phone. Jin catches up to Mikhail and grabs the satphone out of Mikhail's hand. "You stole this?" Charlie says. "How could you respect me if I didn't try?" responds Mikhail. Charlie then threatens to take Mikhail's other eye, but Desmond splits them apart and allows Mikhail to leave because he gave Mikhail their word.
Back at the Staff, Sun admits to Juliet that Jin was infertile when they were off the island and she is certain that the baby isn't Jin's. Juliet tells her that, on the island, a male's sperm count is five times greater than it is off the island and, thus, it is very likely that she could have been impregnated by Jin when they were on the island. "I lose either way," Sun says, "If I'm going to live, that means the baby's not Jin's."
Flashback: At their apartment, Jin finds the money in Sun's purse while looking for the mail key. Sun lies and tells Jin that it is from her father so that they can buy furniture and have a nice honeymoon. Jin is embarrassed that Sun had to do something like that and he tells her that, although it will take longer, he will be able to pay for those things. He tells her that he will always take care of her and to give the money back to her father. "I don't want to be in your father's debt any more than we already are," he says.
Juliet finishes the ultrasound and tells Sun that the date of conception was about eight weeks ago. She was impregnated on the island. And, although Sun begins to cry, all she can do is smile and say, "It's Jin's." Nevertheless, Sun is going to die.
Flashback: In Korea, at the same park where the flashbacks began, Sun meets with the woman whom she had met before. This time, however, Sun knows more about this woman. After she hands her the money, Sun asks the woman straight out, "Why didn't you tell me you were Jin's mother?" "I gave birth to him, but that does not make me his mother," the woman says. In the end, although she gives Jin's mother the money she asks for, Sun tells her, "My husband believes that you are dead; do not force me to make that a reality."
Juliet tells Sun that most of the women made it into their second trimester and, therefore, based on where she is in the pregnancy, she has about 2 months. Juliet changes the subject right away and tells Sun that she needs to go back down to make sure that everything is cleaned up. Down in the station, Juliet walks into the hidden room, opens up one of the lockers and pulls a tape recorder. Juliet proceeds to record the following: "Ben, it's six am on Saturday morning. Kwon is pregnant; the fetus is healthy and was conceived on island with her husband, he was sterile before they got here. I'm still working on getting samples from the other women. I should have Austen's soon. I'll report back when I know more." But off the record, she says, "I hate you."
Back at the landing site, Desmond, Jin and Charlie finish up a stretcher they've made for the parachutist while Hurley keeps an eye on her. Desmond and Charlie discuss whether or not they should've really let Mikhail go, but Desmond believes that, although we should trust them, we've killed more of them then they have of us. "They started it," replies Charlie.
As Hurley acts like he is talking to his mother on the satphone, the parachutist, Naomi, wakes up. She wants to know where she is and Hurley tells her that he doesn't know, but that she's on an island. Their conversation is as follows:
Parachutist: Who are you?
Hurley: Hugo Reyes. I crashed here on Oceanic Flight 815. A bunch of us survived. Is that why you're here? Were you looking for us?
Parachutist: 815. Flight 815, the one from Sydney?
Parachutist: No, that's not possible.
Hurley: Yeah, I know. It wasn't easy, but we found food and a hatch and more food--
Parachutist: No. No, Flight 815. They-- they found the plane. There were no survivors. They were all dead.