Set in the 24th century, the series follows the adventures of the Federation starship Voyager during its journey home to Earth, having been stranded tens of thousands of light-years away. In this episode, Seven of Nine (Jeri Lynn Ryan) is recruited from the future to prevent the present-time destruction of her ship.
A 29th century Starfleet vessel, the timeship Relativity, is attempting to stop the detonation of an explosive planted on Voyager during its travel through the Delta Quadrant in the 24th century, which is causing a time paradox. Captain Braxton (Bruce McGill) and his crew are unable to detect where on Voyager the explosive is located, so they recruit Seven of Nine, pulling her out of the time stream moments before Voyager's destruction, as her enhanced Borg visual sensors can aid in the device's detection. Seven is sent back in time, disguised as a Starfleet ensign, to the point where Voyager is still in drydock prior to her maiden voyage and being inspected by Captain Kathryn Janeway (Kate Mulgrew). Janeway detects Seven's anomalous presence just as Seven locates the bomb. Relativity recalls Seven before she is discovered, but the travel through time kills her on return.
Knowing where the bomb is located, Relativity recalls a slightly earlier version of Seven, and after explaining the scenario, send her back again, now to a point where Voyager has been pulled into the Delta Quadrant and fighting the Kazon, prior to when Seven had joined its crew. Seven's presence is discovered by Voyager, and she is captured; Janeway recognizes her from drydock. Seven explains the situation to Janeway, and together they locate the device, discovering that it was planted by a future version of Braxton himself.
Seven is able to jump back in time to try to stop Braxton from planting the device, but he escapes to the day that Voyager would be destroyed. Seven follows, but the stress of time travel has taken its toll on her body; nevertheless, she is able to warn the Voyager crew of the problem and to apprehend Braxton. The crew of the Relativity, having taken their Braxton into custody as well, pull a version of Janeway like they did with Seven, and send her back to the past at the Kazon attack, where she is able to secure Braxton before he can plant the device. The crew of Relativity pull the time traveler back to their present, re-integrating the various copies with themselves. It is learned that Braxton, after the events of "Future's End", had to spend several months of therapy before being re-assigned for duty, and started to blame Voyager for all the problems that he encountered as they patrolled the time streams, seeing its destruction as a means to end his suffering. Lieutenant Ducane (Jay Karnes), one of Braxton's officers, sends Janeway and Seven back to their proper time streams, allowing them to retain their memories of the events but ordering them never to discuss them with anyone.