In s1-ep2 "Pilot, Part 2", Sayid fixes the transceiver that Jack recovered from the cockpit of Oceanic flight 815, but is unable to pick up a signal on the beach because of interference from the mountains. Sayid decides to hike up into the hills to get better reception, and is joined by Kate, Charlie, Sawyer, Boone and Shannon. After they have walked high enough into the mountains, Sayid checks the radio for a signal and hears feedback, indicating that they have a signal, but are unable to transmit a mayday call because another transmission is already using the frequency from somewhere on the island. The group hears the voice of a French woman repeating a message over and over, and a computerized voice giving a numbered iteration, indicating how many times the message has played. Boone informs the group that his sister Shannon can speak French, and after her initial protests she reluctantly translates the message as: "Please help me. Please come get me...I'm alone now, on the island alone. Please someone come. The others, they're, they're dead. It killed them. It killed them all." Sayid determines from the number of iterations and the length of the message that it has been playing continuously for 16 years and 5 months.
In s1-ep9 "Solitary" Sayid leaves the survivors over his guilt from having tortured Sawyer. During his journey, Sayid discovers a cable in the sand that leads from the water inland and follows it into the jungle. In the jungle, Sayid encounters a tripwire and tries to carefully maneuver across it, but gets caught in a trap and is left hanging upside down for several hours. Sayid is finally cut down by a mysterious person that he sees approaching him with a knife before he falls unconscious.
As Sayid wakes, he finds himself tied to a metal bed frame with an interrogation light shining in his eyes, with a voice repeating "Where is Alex?" When Sayid states that he doesn't know what the person is talking about, a woman moves quickly and does something that electrocutes Sayid. He is tortured in this way several times, before revealing to the woman that he is the survivor of a plane crash, and that he followed a cable from the beach thinking it might have something to do with the transmission his group picked up on the radio. A signal that has been playing for 16 years. A woman steps out of the shadows revealing herself to Sayid for the first time, and repeats the message from the transmission. Sayid realizes that this is the French woman from the distress call. She expresses disbelief that it has been repeating for that long, before knocking Sayid out with the butt of her rifle.
As Sayid comes to, he sees the woman going through his backpack and calls her by the name he sees written on a jacket next to his bed: Rousseau. He asks Rousseau where he is, and questions where she got the power to transmit her distress call for so long. She tells him that she broadcast it from another place now, but that it is controlled by someone else. Rousseau finds pictures of Nadia, Sayid's love, in his backpack. Rousseau asks Sayid to tell her more about who Nadia is. After Sayid tells her that Nadia is dead, because of him, Rousseau shows him a music box that she received from her husband Robert for their anniversary. She says that it had been a comfort to her in the first few years she was on the island, but explains that it no longer works. Sayid offers to fix the music box if she will free his hands. Rousseau injects Sayid with an unknown substance from a syringe, rendering him unconscious yet again.
Sayid suddenly wakes up and finds himself chained to a chair. Rousseau apologizes for sedating him, but explains that it was the only safe way for her to move him. She reminds him of his offer to fix the music box, and he agrees to help, if she will tell him her first name. She replies that her name is Danielle. As Sayid is fixing the music box, he begins to question her about how she came to be on the island.
Danielle tells Sayid that she was part of a science team that was shipwrecked on the island during a bad storm. Her team was 3 days out of Tahiti when their instruments malfunctioned and the ship ran aground. The team was on the island for nearly 2 months before becoming infected by something on their way back from "The Black Rock". Danielle claims the 'Others' were the carriers of the illness. Sayid asks her if she has seen other people on the island, but she claims to have only heard them whispering in the jungle. At this point, Danielle hears a sound from outside the bunker and leaves to investigate, armed with her rifle. Sayid seizes this opportunity to escape from the chains holding him to the chair. Sayid takes the maps Danielle has in her shelter and follows her into the jungle, armed with another of her rifles.
Sayid confronts Danielle in the jungle and tells her to drop her weapon. Instead, she levels her rifle at him. When Sayid tries to fire, Danielle tells him that the firing pin had been removed, and that Robert hadn't noticed it missing either when she shot him. She explains to Sayid that her team had become sick, one by one, and that she had killed them all. She also tells Sayid that Alex was her child. After unsuccessfully trying to convince Sayid to stay with her, she warns him to keep a close eye on the other survivors.
In s1-ep12 "Whatever the Case May Be." Sayid returns to the survivor's camp with the maps, and asks Shannon to translate the French writing on them. When Shannon translates the writing as "the sea of silver sparkles that change...next to the pond....blue infinity", Sayid becomes frustrated and quits trying to make sense of the maps. Shannon later comes to Sayid and tells him that she recognizes the words as lyrics to the song "La Mer", from the French-dubbed version of "Finding Nemo."
In s1-ep18 "Numbers", Hurley sees his unlucky lottery numbers written on Danielle's maps in Sayid's tent. Hurley returns that night and steals the maps, setting off into the jungle to try to find her. Hurley goes looking for confirmation that the numbers are indeed cursed. Charlie, Jack and Sayid go off after him and eventually catch up to Hurley, who tells them he is trying to get a battery from Danielle. After Hurley and Charlie are separated from Jack and Sayid, they find themselves under fire, and Hurley comes face to face with Danielle, who is pointing a rifle at him. He shows Danielle the map he took from Sayid, and asks her what the numbers mean. Danielle tells Hurley that she doesn't know the meaning of the numbers. She tells him her team's ship had picked up a transmission of the numbers repeating. Her team changed course to investigate the transmission, before becoming shipwrecked. Once on the island, her team searched for the transmission source for weeks before finding a radio tower by "The Black Rock". After her team became sick, Danielle went to the tower and changed the transmission to her distress call. When she agrees with Hurley about the numbers being cursed, he hugs her in relief that someone doesn't think he is crazy. Hurley later returns to his group with a battery from Rousseau, and a message for Sayid: "She says, hey".
Rousseau comes to the beach camp in s1-ep23 "Exodus-Part 1" to warn the survivors that the "Others" are coming. She tells the group that when her ship went aground 16 years ago, she was 7 months pregnant and delivered the infant herself. After spending one week together with the newborn, she saw a pillar of black smoke 5 kilometers inland. Danielle states that night, the "Others" came and took her baby girl, Alex. She tells the survivors they have 3 choices: run, hide or die. Jack is skeptical of Danielle's warning until Walt points out a pillar of black smoke to the group. Jack, Locke, Sayid and Hurley go to Danielle for more information. They take her to the hatch and suggest it as a possible hiding place for the survivors, but explain that they have no way of opening the door. Locke asks Rousseau if she has any more explosives from when she booby-trapped her shelter. She tells them that there is dynamite by "The Black Rock", in the Dark Territory and agrees to lead them to it.
Jack, Locke, Kate, Hurley and Arzt follow Rousseau through the jungle in their quest for the dynamite. At one point, Danielle tells them they have reached the Dark Territory, where her team became infected and where Montand, presumably a member of her team, lost his arm. The group hears the sounds of the monster and Danielle tells them it is a security system for the island. Once she leads them to "The Black Rock", which is a large wooden sailing ship located several miles inland; Danielle disappears into the jungle once again.
In s1-ep24 "Exodus-Part 2" Rousseau returns to the beach camp, supposedly looking for Sayid. Mesmerized by Claire's baby, Danielle asks to hold him, but Claire refuses. As Claire looks at some scratches on Danielle's arm, she has a memory of scratching Danielle while kidnapped and asks Danielle why she scratched her. The next time we see Claire, she is awakening on the beach with a bloodied head and her baby missing. It is presumed by everyone that Danielle took the baby, and Sayid and Charlie go after her armed with guns from the Marshall's case.
Charlie is tricked into believing one of Danielle's booby traps is the missing baby in s1-ep25 "Exodus-Part 3" and is hit in the head by a load of rocks. Sayid cauterizes the heavily bleeding wound with gunpowder and a match before they continue their hunt for Rousseau and baby Aaron. They finally reach a distant beach and see the black smoke billowing from a pyre on the sand. The beach is deserted, but they hear the baby crying and call Danielle out of her hiding place in the shadows. She tells Sayid and Charlie that she had brought the baby to the beach, hoping to trade him to the "Others" for her daughter, Alex. She turns Aaron over to Sayid, who hands him to Charlie. Danielle told them she had heard the "Others" whispering, saying that they were coming for the child, that they were coming for the boy. Unknown to any of them, the "Others" were actually coming for Walt on the raft. Charlie and Sayid returned Aaron to Claire that night.
Sayid and Hurley hear Danielle's transmission again in s2-ep13 "The Long Con" with the radio from the arrow station, before picking up a broadcast of the Glenn Miller Orchestra playing "Moonlight Serenade" from station WXO.
Ana spots Danielle in the jungle in s2-ep14 "One of Them" and attempts to find Jack, instead encountering Sayid. Ana takes him into the jungle and Sayid sends her back, preferring to approach Danielle alone. Rousseau tells Sayid that she had been looking for him, that she needed to take him somewhere to show him something important that would help him. When Sayid expresses distrust in Danielle's motives, she gives him her rifle. Continuing through the jungle, Danielle finally stops and uncovers a handmade crossbow and arrows that she's hidden in the brush. She tells Sayid that they are at their destination, when Sayid hears a man's voice calling for help. He runs toward the voice as Danielle tries to stop him. Sayid discovers a man hanging from a tree in a net trap, pleading for help. The man tells Sayid that Danielle is crazy and trapped him the night before. Sayid cuts him down from the trap as Danielle insists that the man is one of the "Others" and is lying. Danielle readies her crossbow, and as Sayid helps the man up, he tries to run away. Rousseau shoots him through the shoulder from behind with one of her arrows as he flees. She tells Sayid to take him to the doctor to be treated for his injury and then to interrogate him, but warns Sayid that the man will lie for a long time.
In s2-ep15 'Maternity Leave', Danielle approaches Claire on the beach while Claire is trying to comfort baby Aaron, who has become ill with a fever and a rash. Danielle asks Claire if the baby is infected, and tells Claire the child is sick. Claire has a flashback and recalls a struggle with Danielle in the jungle that occurred during Claire's kidnapping and assumes that Danielle was trying to take her back to the Others after she escaped from them. Claire and Kate track down Danielle in the jungle and Claire demands to be taken to the place she remembers from the flashbacks. Danielle takes them to the spot where Claire scratched her, and asks Claire where they should go next. Claire and Danielle begin to fight and Kate draws a gun on Danielle, telling her to get her hands off Claire. Danielle approaches Kate until the barrel of the gun is up against her chest, and tells her, "Go ahead, please. Do it." Kate leaves Danielle in surprise and follows Claire deeper into the jungle. When the three women find and go inside the Dharma Cadeceus Station, Claire and Danielle search for the medicines Claire wants for the baby while Kate explores another area. Claire has another flashback from her kidnapping and realizes that Danielle was actually trying to help rescue her from the Others, and that she scratched Danielle while under the influence of some unknown drug that she had been given by Ethan to sedate her. Danielle hit Claire in the head with the butt of her rifle and knocked her unconscious when Claire was still struggling with Danielle. When Claire tells Danielle that she remembered what really happened, Danielle told her that she had carried Claire on her back to her camp and left her where she would be discovered by the survivors. The three women left the station after being unable to discover any medicines and headed back towards camp. Danielle stayed with them for part of the trip, before saying that she would not go any farther with them. Claire told Danielle that a teenaged girl with blue eyes had helped her escape from the Others, and that the girl wasn't like the Others, that she was good. After telling Claire that she was sorry they didn't find what they were looking for, Danielle told Claire "I hope you're baby's not infected. But if it is, I hope you know what must be done." Danielle then disappears into the jungle once again.
Danielle's whereabouts throughout much of the time on the island remain a mystery, as does the illness that infected her team. She is skilled at tracking and hiding, and in weaponry and camouflage. It is unknown what kind of science her team was involved with, or how much of what Danielle even says can be trusted, as her mental health has been called into question several times.
