In 2374 the remains of Lyndsay Ballard were found drifting in space by the Kobali, a Delta Quadrant species. After re-animating her, they told her that she was dead, but she refused to believe it until they showed her a scan of her corpse lying inside a torpedo casing. In the coming months they changed her Human form into a Kobali form by altering her DNA. When the transformation was complete, she was given the Kobali name Jhet'leya and placed in a Kobali family to help her acclimate.
Although raised from the dead and transformed to Kobali, she still possessed some memories of her former Starfleet life and wanted to contact USS Voyager. However, the Kobali told her that they were part of her kyn'steya, her past life, and that she would need to forget all of them, but she couldn't. It took two years before her Kobali family trusted her enough that she felt she could risk an escape attempt. In mid-2375 she stole a Kobali shuttle and went to search for Voyager.
In 2376, after fighting off an attack by two Kobali ships, she made contact with Voyager via Mezoti in astrometrics. After Mezoti accidentally closed the channel on her, she hailed Voyager again and spoke with the now Lieutenant Commander Tuvok.
She rendezvoused with Voyager and told Captain Janeway that she was Lyndsay Ballard and wanted to return to Voyager. After some deliberation, Janeway decided to let her come aboard, beaming her to sickbay where The Doctor could examine her. During a lengthy conversation between her, Harry Kim, and Captain Janeway, she tried to prove who she was, but eventually it was The Doctor who found traces of Human DNA which matched the genetic samples of the deceased Lyndsay Ballard. Due to the presented evidence, Captain Janeway decided to accept her explanation as true and welcomed her back on Voyager.
After the senior staff welcomed her back, Kim escorted her to her quarters where Neelix and Tom Paris had already brought Lyndsay's personal effects. She told Kim that she had made a list of things to do when she got back to Voyager and that hearing him play was #26 on her list. Some other points were #6, taste a Jibelian berry salad, #16, dazzle Lieutenant B'Elanna Torres, #27, show up on time for a duty shift, and #32, make Tuvok laugh.
While Kim and Ballard were reminiscing on the past, they were interrupted by The Doctor, who told them that Ballard's Human form could not be brought back because her DNA had been altered too much. Fortunately, her appearance could be restored using inaprovaline, although only for short periods of time.
When she resumed her assignment in main engineering, she showed up on time and, by solving an alignment error in the dilithium matrix, even dazzled Lieutenant Torres, though she could not prevent herself from speaking Kobali while solving the problem. By the time that Kim visited her in sickbay, The Doctor had restored her Human appearance.
Captain Janeway invited her to a dinner date, which went horribly wrong when she started babbling to the captain and insulted her pot roast. She later had a nightmare where her colleagues question her coming back to Voyager. When asking Kim for advice, she somehow knew that the Kobali had found her.
When the Kobali ship contacted Voyager, Jhet'leya's father Q'ret asked to speak to her. He was startled by her Human appearance and asked why she left the Kobali. When she explained that she belonged on Voyager, Q'ret told them that during the re-animation and transition to Kobali residual memories of a former life might remain. He told her that she was his daughter, and that the moment the remains of Lyndsay Ballard where found they acted according to Kobali customs. The remains were used to create Jhet'leya; Lyndsay Ballard died three years ago. When Q'ret asked her what he should say to her sister Tynsiya, she responds, "tell her that her sister is dead," and left the room. When Captain Janeway told Q'ret to leave, he warned that he'd be back for her, despite the fact that his ship wasn't nearly a match for Voyager.
When Kim found Ballard in the mess hall having a midnight snack, she was considering what Q'ret had said. When Kim asked about her Human father, Professor Ballard, she couldn't even remember him. When they left the mess she doubled over as her Kobali appearance started to reassert itself. The Doctor confirmed that he could not maintain her Human appearance without increasing the daily dose of inaprovaline, which she couldn't handle, and she started yelling at him in Kobali before storming out of sickbay. Later Kim told her that he wanted her to stop the treatment, and that he didn't care if she looked Kobali, but she no longer believed she was doing the right thing. She said that she didn't belong on Voyager, and that the feeling was with her since she returned. She decided to return to the Kobali, and explained to Kim that Lyndsay Ballard, the girl he was in love with, died three years ago. She could no longer deny this.
Q'ret was joined by two other Kobali ships and began to attack Voyager, nearly defeating it, as Ballard and Kim went to the bridge. She yelled that she did not want to stay, as she did not belong on Voyager. She agreed to go with the Kobali if the attack would cease. Kim was reluctant, but she told him that at least they now had the time to say goodbye.
When The Doctor stopped his treatment, her Kobali appearance returned and she was ready to leave her old life behind. Before stepping onto the transporter pad, she told Kim that at least she took care of all the important things on her list. (VOY: "Ashes to Ashes")