Before Oceanic 815Rachel, became her first human test subject. However, Juliet treated her sister in secret until her ex-husband, Edmund, who was also her supervisor, discovered what she was doing. He attempted to blackmail Juliet into working with him in exchange for keeping quiet about the possible ethical concerns. Richard Alpert, a representative of Mittelos Bioscience, courted Juliet in bringing her on board to further her work, but Juliet declined as Edmund wouldn't allow her anything. Juliet commented that he would have to be hit by a bus for her to leave. After the fertility treatment worked on Rachel, Juliet went to see Edmund. As they were talking about Rachel's pregnancy and the treatment, he stepped onto the road and was suddenly hit by a bus. At the morgue, Richard Alpert and his associate, Ethan Rom, met with Juliet and asked her once again to come work with them.
Agreeing to Alpert's offer, Juliet signed confidentiality agreements and other paperwork for a six month stay at their facility, allowing her to return before Rachel gave birth. She did some research and discovered that no one in the medical community had heard of Mittelos Bioscience, but deep down she knew the place she was being taken to was special, and Alpert assured her she would see things there she could never have imagined. Due to the trip to the island being "intense", as Ethan put it, Juliet was tranquilized. She awoke aboard the Others' docked submarine and was greeted by Benjamin Linus. Ben provided her with her very own house at the barracks in the central part of the island.
Juliet learned she was recruited due to a problem the Others were having — all their pregnant women were dying. During the second trimester when the mother's immune system is triggered, the white blood cell count plummets and the immune system seems to turn on the fetus. She worked with Ethan at The Staff to find a solution, but only witnessed many deaths from the mysterious problem. Six months into her stay, Juliet came to the conclusion that the problem occurred only with women who conceived on the island and, if so, there was nothing she could do about it on the island. Ben refused to allow her to take one of the pregnant women off the island to prove her theory, so she asked him to let her go home. However, Ben informed her that Rachel's cancer returned and she was going to die. He offered to cure Rachel's cancer, claiming that Jacob would take care of it himself, in exchange for her staying on the island and finding a solution to their problem. Juliet agreed to his offer.
Spending another two years and six months on the island in search of a seemingly unattainable solution, Juliet settled into life with the Others and grew close to Goodwin who worked at the Tempest. Despite the fact that Goodwin was married to Harper, Juliet's on-island therapist, the two had an affair. Julet and Harper never got along very well, and this only got worse when Harper found out about the affair. She confronted Juliet, warning her there would be consequences and Goodwin could be hurt by Ben, who wanted Juliet for himself. But Juliet and Goodwin continued their relationship in private as Goodwin was dismissive of the idea Ben going to do anything about it. Ben later came to Juliet with a pain in his back and had X-rays taken. Through these X-rays, Juliet discovered he had a large tumor on his spine. Told that no one on the island has developed cancer, Juliet believed Ben had lied to her about curing Rachel and confronted him. She wanted to go home to see Rachel, but Ben refused to allow it and maintained that he didn't lie about curing her sister's cancer.
After Oceanic 815
The First 65 Days
The following day, Juliet was in the middle of a book club meeting with several Others at her house when they experienced a tremor. She and the group rushed outside to see the cause of the tremor when they witnessed Oceanic flight 815 breaking apart overhead. After Ben sent Goodwin and Ethan to infiltrate any survivors, Juliet was taken to The Flame. Mikhail Bakunin used the stations systems to uplink to Alpert who was filming a very much alive Rachel and her baby son. Ben wanted to prove to Juliet that he never lied to her, but refused to let her go home until she found a solution to their problem. She still believed it was impossible, but Ben told her they would keep finding more mothers until she found a solution.
One such mother came in the form of Oceanic survivor Claire Littleton. Blood samples taken by Ethan revealed she had the same symptoms as the women who conceived on the island. Juliet developed a serum to keep Claire alive during the late stages of her pregnancy, and Ethan administered the serum to her. The baby was important to the work in finding a solution, but Claire managed to escape with the help of Alexandra Rousseau and Ethan was killed while attempting to recover her. However, Juliet's serum seemingly worked as Claire and her baby lived, but her survival may be due to having not conceived on the island. With news of Ethan's death having reached the barracks, Juliet wanted Ben to bring Goodwin back from his infiltration of the tail-section survivors. She didn't believe it was necessary for him to be there any longer since they already took everyone from the list. Ben told her Goodwin was making a case for one of the survivors, Ana-Lucia Cortez, and was going to keep him out there for a little while longer. However, the survivors discovered Goodwin's true identity and he was killed. Ben took Juliet out to the jungle and showed her Goodwin's body. Juliet realized that Ben had purposefully kept Goodwin in danger and that he knew Goodwin would eventually get killed. Juliet couldn't understand why Ben would do something like that. Ben got furious and told Juliet that she belonged to him.
With the capture of Jack Shephard, Juliet became his jailer during his stay inside The Hydra. Ben chose Juliet for this role as he believed she bore a striking resemblance to Sarah, Jack's ex-wife, and believed it would help Juliet gain Jack's trust. Juliet shared detailed information about Jack's life prior to the Oceanic crash. She offered to tell Jack anything he wanted to know and, after he requested to know if his ex-wife was happy, told him she was. During her time gaining Jack's trust, Juliet prevented the escape of James "Sawyer" Ford after he was freed by Karl. She was also seen at a construction site that the Others are making Sawyer and Kate Austen work at. During one of her visits there she prevented another escape attempt by Sawyer by threatening to shoot Kate. Afterwards, Sawyer confided to Kate that Juliet would have definitely shot and killed her.
Jack eventually learned that he was taken to perform spinal surgery on Ben. He refused, but Juliet tried to convince him to go through with it, secretly informing him via cue cards that Ben was a liar and very dangerous. She wanted Jack to let Ben die and make it look like an accident. Jack eventually agreed and Juliet assisted in the surgery, but Jack made an incision in Ben's kidney sack and held him hostage in order to free Kate and Sawyer. Ben awoke from the anaesthesia and offered to let Juliet finally go home if she helped Jack's friends escape and let him live. Juliet accepted Ben's offer, but was forced to shoot and kill Danny Pickett when Pickett refused to let Sawyer go. This action has severe consequences as she was put on trial and condemned to be executed. Her life was saved when Jack agreed to help monitor Ben's condition and nurse him back to health if he saved Juliet's life. He agreed, but ordered to have Juliet marked instead of executed, leaving a marking burned into the flesh of her back.
As Jack's friends knew where to find The Hydra, the Others abandoned the station and returned to the barracks. Ben kept good to his word and about a week later he allowed Juliet and Jack to use the submarine to leave the island. However, Jack's rescue party found the barracks and John Locke used C-4 explosives from The Flame to destroy the sub. With her means to go home destroyed, Juliet agreed to a plan by Ben to infiltrate the Oceanic survivor's beach camp by appearing to have been left behind by the Others. While the other survivors were wary of Juliet, Jack vouched for her and allowed to her come back to the beach camp. An implant placed inside Claire during her stay at The Staff was activated by Ben, causing her to become violently ill. Juliet used a serum to "save" Claire, thereby easing the survivor's doubts in her and helping to further her infiltration.
After seeing Sun-Hwa Kwon's unborn child on an ultrasound, Juliet had second thoughts and informed Jack to the true nature of her being left behind by the Others. She was to mark the tents of the pregnant women and the Others were to raid the camp and take them. Tired of running from the Others, Jack hatched a plan with Juliet and Danielle Rousseau to booby trap the marked tents with dynamite from the Black Rock. While the trap was to be sprung on the Others, the survivors were to head to the radio transmitter on the island to turn off Rousseau's distress signal and then contact Naomi Dorrit's off-shore freighter with her satellite phone. However, Juliet revealed the existence of The Looking Glass, an underwater DHARMA station that was jamming all communication to and from the island. Desmond Hume and Charlie Pace volunteered to deactivate its jamming equipment while Juliet accompanied Jack, Danielle and the other survivors to the radio transmitter. That night the survivors witnessed the explosions from the trap, but something went wrong as not all three explosions were triggered. Juliet volunteered to go with Sawyer back to the camp and watched as Sawyer shot Tom in cold blood.
A second helicopter arrived from the freighter carrying Daniel Faraday, Miles Straume, Charlotte Lewis and Frank Lapidus. The survivors split into two groups: those who believed Charlie's warning went with John Locke to the barracks while those who believed in rescue stayed with Jack Shephard. Juliet stood by Jack, and their group eventually met with Daniel and Charlotte. Locke's group made it to the barracks with Benjamin Linus as prisoner. Despite being held prisoner, Ben relayed a message to Juliet through Harper. Daniel and Charlotte disappeared into the jungle and Ben's message claimed they were heading to the Tempest to kill everyone on the island. Juliet traveled to the station to stop them, but learned they were trying to render its toxic gas inert to prevent Ben from using it against them. Daniel managed to secure the station and its threat. Jack caught up with Juliet and learned Ben believed she belonged to him and would try to kill him. However, Jack had feelings for her and wasn't intimidated by Ben.
- Information is shown in chronological order. Episodes in bold are flashback episodes.
Before the Crash
- 3x07 - Not in Portland: Is recruited to the island by a Mittelos Bioscience representative and Ethan Rom.
- 3x16 - One of Us: Is brought to the island by Ethan and learns what she's there to do.
- 4x06 - The Other Woman: Has an affair with Goodwin.
On the Island
- 3x01 - A Tale of Two Cities: Juliet attempts to get Jack to co-operate.
- 3x02 - The Glass Ballerina: Juliet prevents another escape attempt by Sawyer.
- 3x05 - The Cost of Living: Juliet asks Jack to assassinate Ben.
- 3x06 - I Do: Juliet assists Jack in Ben's surgery.
- 3x07 - Not in Portland: Kills Danny Pickett and lets Ben live.
- 3x09 - Stranger in a Strange Land: Is spared her life for the killing of Pickett, but is instead marked.
- 3x16 - One of Us: Is taken back to the beach camp and begins her infiltration of it.
- 3x18 - D.O.C.: Takes Sun to The Staff and discovers that her baby was conceived on the island with Jin. Informs Jack of what Ben was making her do.
- 3x16 - One of Us: You know what's interesting? That you two are the camp's moral police. I'm curious, Sayid... How long was it before you told everyone on that beach exactly how many people you've tortured in your life? Do they know about Basra? And I'm sure the first thing you did when you got here, James, was to gather everyone in a circle and tell them about the man you shot in cold blood the night before you got on the plane. So why don't we just skip the part where you two pretend to be righteous? I'm taking that medication back to Claire and you're going to let me, because if she doesn't get it, she's going to die. And the last thing that either of you need right now... is more blood on your hands.
- 3x01 - A Tale of Two Cities: It doesn't matter who we were. It only matters who we are.