Kes lies on a bed in Sickbay, elderly and confused. A little boy is keeping vigil at her bedside, but she doesn't know him. He's her grandson Andrew, and he offers her a present that he's just made for her, but becomes upset when he realizes she just does not remember him. The Doctor prepares to extend Kes' dwindling lifespan in a biotemporal chamber.
In a flash, Kes awakens in her own bed back in her quarters. Andrew is there, working on a present for her. A young woman is there with him, but a disoriented Kes must be reminded about who she is. It's Linnis, Andrew's mother and Kes' grown daughter. A concerned Linnis guides Kes to Sickbay where the Doctor breaks the bad news. Kes is experiencing mental deterioration because she has reached the morilogium - the final weeks of life. Kes is nine years old, which is a ripe old age for an Ocampan. Tom Paris and Harry Kim rush in. Tom must remind her that he is her husband. Harry is married to Linnis and is Andrew's father. As the family squabbles over Kes' end-of-life decisions, she flashes out of the room and new surroundings appear around her.
It's her birthday party. She is turning nine and her grandson Andrew is planning to make her a special present. He apologizes for not having started it yet, but Kes expects him to say something like that. She seeks out the Doctor and explains the strange things going on. She remembers things that have not happened yet, and everyone else seems to remember years' worth of events she never saw. As she works with husband Tom to figure out what has happened to her, he reminisces about the happy marriage Kes doesn't seem to remember. He fills her in as best he can. Tom fell in love with Kes after she helped him recover from the death of his lover, B'Elanna Torres. She was killed during the "Year of Hell", a time when Voyager was struggling through a hostile territory of a race called the Krenim and endured constant attacks. Captain Janeway and many other members of the crew also died. As he remembers this painful time Tom recalls that the weapons being used against Voyager during these battles soaked the ship with chroniton radiation, a form of energy with temporal properties. Just as they suspect a link between these temporal weapons and Kes' temporal jumps, she flashes into a new room on a different day.
Andrew has just been born. A younger Kes is clear-headed enough to begin to put the pieces together. She rushes to the Doctor and pours out her story. They understand that she is hopping back through time and the biotemporal chamber in which the Doctor treated her on the day she died has reactivated her life - only in reverse.
Suddenly, Kes is giving birth. Linnis is born during a fierce space battle that Voyager barely survives. As Kes holds her new daughter in the wreckage of the ship and considers what to do, she flashes out once more.
She finds herself at a cheerful party on the holodeck. Tom is there, but she can see that he is not yet her husband when he sweeps B'Elanna into an embrace and kisses her. The party is cut short when Voyager is attacked out of nowhere by an unidentified force firing chroniton-based weapons. The crew race to the bridge and Kes tries to tell Captain Janeway what's going on but has no time to explain how she knows. Janeway joins B'Elanna at her work station where they try to defend the ship against the attack. An explosion rocks the bridge and both are killed. As Kes weathers the crew's grief and the ship's damage, she calculates the temporal variance of the weapon that caused all her troubles - it is 1.47 - and memorizes it before her next jump.
She arrives at a time when the crew is alive and well, and free to help her. Before they put her in the biotemporal chamber to reverse her problem, Kes tells Janeway about the Krenim and to be careful.
She eventually meets up with her father during one of these jumps, who talks to her about being late to the dinner table. Kes's father is played by Michael Maguire.