"Across the Sea" is the fifteenth episode in Season 6 of Lost and the 118th produced hour of the series as a whole. It aired on May 11, 2010. The history of the relationship between Jacob and the Man in Black is revealed.
About two millennia before the crash of Flight 815, a woman named Claudia surfaces from the ocean and clings to the remains of a ship. She looks around and sees an Island. Eventually she is washed ashore and as she struggles to her feet her billowing red dress reveals her advanced pregnancy. The beach is strewn with debris from the shipwreck. She makes her way inland and drinks from a stream. As she drinks, she is startled to see a woman reflected in the water. The woman takes Claudia to her primitive camp, feeds her and treats her injuries. The two have a conversation in Latin, and the woman answers Claudia's questions, telling her that she is alone and that she also arrived "by accident." Claudia begins to ask many questions to which the woman finally responds that every question Claudia asks will only lead to another question, and suggests that Claudia should just rest and be grateful she is alive. Claudia says she wants to look for other survivors from her boat but the woman firmly denies it, saying that if there are any other survivors, she will find them. Moments later, Claudia goes into labor with the woman acting as midwife. A beautiful boy, whom Claudia names Jacob, is delivered. Then another boy is born. Claudia says that she had only picked one name. The woman cares for the babies — swaddled in light and dark material — with concern. When Claudia asks to see the second boy, the woman only says, "I'm sorry," and kills Claudia by a blow to the head with a rock.
Thirteen Years Later
The Boy in Black finds an Egyptian Senet game on the beach. Jacob runs up to him, and the Boy in Black tells him about what he found. He explains that it is a game and that he "just knows" how to play. He agrees to play with Jacob, but only if Jacob doesn't tell their mother because he believes she will take the game away from them.
The same day, Mother is working at her loom and she asks Jacob whether he loves her. He says he does and she says "Then tell me what happened." She joins the Boy in Black on the beach and he immediately guesses that Jacob told her about finding the game. Mother says that Jacob doesn't know how to lie. She tells the Boy in Black that he is "special." She says that it was she that left the game for him. The Boy in Black says that he thought it may have come from "Somewhere else, across the sea." She tells him that there is nowhere else, that the island is all there is. The Boy in Black asks where they came from, to which Mother replies that the brothers came from her and she came from her mother, who is dead. The boy asks what "dead" means. His mother says that it is something that he will never have to worry about.
The boys chase a boar, but are surprised when it is killed by three hunters. The twins run home and demand an explanation as to who these people are from Mother. She says that these men are not like them because "we are here for a reason." The Boy in Black insists on knowing what the reason is. Mother blindfolds the boys and leads them into the jungle. She tells them that the other people are dangerous because they come, they fight, they destroy, they corrupt and it always ends the same. She tells the boys that she has made it so they can never hurt each other. Mother removes their blindfolds and they turn and see a cave with a stream running into it; the cave emits a glowing golden light. She tells them that it is the reason they are on the island. She tells them they must never enter the cave. The Boy in Black says that it is beautiful, she agrees and tells them that a little bit of the same light that is in the cave is inside every man but that people always want more. Mother says that while the other people can't take the light, they might try and if the light goes out here it goes out everywhere. Mother has protected the place but when she no longer can then it will have to be one of the twins who protects it.
Some time after, the boys are playing Senet. The Boy in Black tells Jacob that he can't make a move (sideways) because it is against the rules. He says that one day Jacob can make up his own game and then everyone will have to follow his rules. The Boy in Black notices the appearance of Claudia a short distance away, bathed in light. Jacob does not see her, and his twin excuses himself to go follow. She explains to the Boy in Black that Jacob cannot see her because she is dead. She takes him to a place on the other side of the Island and shows him a bustling settlement. She says the people came from across the sea thirteen years ago. She tells him that she is his real mother and Jacob's mother too and that he comes from across the sea.
Thirty Years Later
Jacob has finished a piece of cloth on the loom. Mother claims tiredness as she grinds herbs. Jacob goes to the other side of the island and observes his brother working at a project with the other people. He goes down to the Man in Black and they talk over a game of Senet. The Man in Black tells Jacob that Mother may be insane but she is right about his people being bad. He says they are greedy, manipulative, untrustworthy and selfish. He explains he stays with them as a means to an end, that is, to leave. The Man in Black reveals to Jacob that he has found a way off the Island. He throws his dagger wildly and it is attracted to and adheres to stone blocks of a well. He talks about the way metal behaves strangely at certain sites around the island and this has suggested a way off the Island. The Man in Black asks Jacob to join him. but Jacob says that the Island is his home and that he doesn't want to leave. The Man in Black says that it is not his home.
Jacob tells Mother that his brother has found a way to leave. Mother goes to see the him and sees that the other people have dug a well. After they leave she enters the well and finds him working. The Man in Black welcomes her coolly and complains how he has searched the Island and has not once come close to finding the cave. He tells her that he then thought about another way to get to the light. He tells Mother that the people have some very interesting ideas about what to do with the light. She gives a look of alarm at the knowledge these people now have. He shows her that he has found a way to dig into the light that exists beneath parts of the Island. He dislodges a stone, allowing the light to stream into the cavern. The Man in Black has constructed a wheel and he plans to dig a large hole into the wall of the well and use it and water to construct a mechanism which will allow him to leave the Island. Mother asks how he knows these things, and with hatred and sarcasm he replies that he knows all of this because he is "special." Mother feigns a goodbye hug and while saying that she is sorry she cracks his head against the brick wall beneath the fissure.
Mother returns to Jacob and takes him to the glowing cave. She tells Jacob that he is going to protect it now. Jacob asks what is inside the cave and Mother says: "Life, death, rebirth; it's the source, the heart of the island." She asks him to promise that he will never go down there because to do so would be much worse than dying. She pours some wine from a flask into a silver cup, making an incantation as she does so. She says that in drinking the wine he accepts the responsibility of protecting this place for as long as he can and then to find a replacement. He is unwilling and is saddened at becoming her successor by default, as she had always favored his brother. She admits she was wrong and that it should have been him all along. Jacob drinks. Mother tells him, "Now you and I are the same."
The Man in Black wakes. His well is wrecked and filled in and he sees smoke afar. He finds the village destroyed and all his people dead. He finds the burnt remains of his Senet game. He staggers around in frustration and anger.
Jacob and Mother are returning home; she says that a storm is coming and sends Jacob off for firewood; she asks him to be careful but does not reply when he says that he will see her back home. At Mother's camp the loom is wrecked and the camp in disarray. Mother finds the game she had left for the Boy in Black thirty years before laying on the ground. As she raises the black playing piece she is run through from behind by the Man in Black's dagger. With tears in his eyes the Man in Black addresses her as "Mother" and asks why she wouldn't let him leave. As she dies she says: "Because I love you... Thank you."
Jacob returns and sees what his brother has done and attacks him as he did as a thirteen year old. He drags his brother through the jungle. The Man in Black reminds him that Jacob cannot kill him. Jacob replies that he has no intention of killing him. He brings him to the glowing cave and throws him down the stream towards the mouth of the cave. The Man in Black hits his head on a rock and goes limp, then is sucked into the source. Moments later the Smoke Monster bursts from the cave and disappears into the jungle. Jacob washes himself at a stream and sees his brother's broken body draped over branches nearby. He hugs him tearfully. Jacob carries his body back home and finds the two jewels and places them in a pouch. He lays Mother and the Man in Black's bodies side by side with the pouch at Mother's hand.
September 28, 2004
Centuries later, seven days after the crash of Oceanic Flight 815, Jack Shephard and Kate Austen discover the corpses laid on opposite sides of the cave, as well as the black and white stones. John Locke calls the pair "our very own Adam and Eve."