TREKCORE > VOY > EPISODES > UNFORGETTABLE > Synopsis

Thanks to StarTrek.com:

A cloaked ship suddenly appears with an injured female onboard hailing Chakotay. Once Kellin, the injured woman, is beamed to sickbay, she asks the Captain for asylum from her people. When Chakotay asks how she knows him, she explains that she was recently on Voyager for several weeks. No one remembers her because memories of her people cannot be held in the minds of others for more than a few hours. Her body produces a pheromone that blocks their long-term memory engrams. She confesses that she has returned to Voyager because she fell in love with Chakotay.

Chakotay informs the rest of the senior staff that Kellin is from Ramura, a closed society that tracks down people who leave their world. She was on Voyager about a month ago when her bounty hunting brought her to a stowaway on the ship. Although Kellin says a computer virus was planted to erase all evidence of her presence, the crew is still ordered to look through navigation logs and other outlets that would corroborate her story. While Kellin recounts to Chakotay how they fell in love, the Ramura begin firing at Voyager.

Janeway gives Kellin permission to modify the ship's sensors so they can see the cloaked ships. Once Voyager returns fire, the Ramurans leave and Kellin says she would like to stay on the ship permanently. Although Chakotay doesn't remember loving her, he can't stop thinking about what she has said about their relationship. When Kellin realizes that her people will come back and that she is putting the crew in danger, she tells Chakotay that she will leave if he doesn't have any feelings for her. However, he tells Kellin to stay.

Reminiscing about their last night together, Kellin explains how Chakotay helped her find the stowaway. They used a magneton sweep to disrupt his cloak, and then Kellin wiped out his memories of the outside world with a neurolytic emitter. Working with Seven of Nine and Kim on a defense strategy against her people, Kellin soon senses that a tracer is onboard. He suddenly materializes, and despite her protest, the Ramuran shoots her with the neurolytic emitter.

As Kellin's memories begin to fade, she begs Chakotay to remind her of the love they shared, once she no longer remembers. Soon, she does not recognize him, and Chakotay tells her about their relationship. He asks her to stay and see if her feelings can be rekindled, but she refuses to violate her people's edict again. Once she and the tracer are gone, Chakotay writes about her in his personal log so he will never fully forget her.