Plot summary
Fifteen years in the future, Chakotay and Harry Kim discover Voyager frozen on the surface of an ice world. They recover the body of Seven of Nine, collect the Doctor via his mobile emitter, and return to the Delta Flyer, joining Chakotay's girlfriend Tessa Omond (Christine Harnos). Kim explains to the Doctor that fifteen years prior, the crew had attempted to use slipstream engine technology to bring Voyager home, with Chakotay and Kim in the Delta Flyer leading the larger ship. However, the slipstream became unstable, causing Voyager to crash into the ice world. Chakotay and Kim have spent the last fifteen years searching for the ship. Kim explains that he can send a message back in time to Seven using a stolen Borg temporal transmitter, which would then prevent the accident.
As the Doctor and Kim work, they are pursued by USS Challenger, commanded by Captain Geordi La Forge. La Forge warns them that he knows they are trying to alter the past, a violation of the Temporal Prime Directive and although he's sympathetic to them, La Forge must stop their efforts. Chakotay offers Tessa the opportunity to be safely transported to the Challenger but she refuses.
The Doctor successfully discovers the correct Borg time index, and Kim sends the information, but this ultimately has no effect on the slipstream, and Voyager is still lost. Kim realizes the changes have not worked and blames himself for destroying Voyager twice. The Doctor convinces him to try again, but with a less optimal solution: to have the changes collapse the slipstream, keeping Voyager stranded in the Delta Quadrant but with all hands alive. As the Challenger opens fire on the Delta Flyer, an overload starts to build in the warp matrix. Kim successfully sends out the signal before the Delta Flyer 's warp core breaches.
In the present, Voyager once again enters the slipstream, losing communications with the Delta Flyer. Seven receives the new calculations, and Janeway orders her to implement them. As planned, this causes the slipstream to fail, leaving Voyager and its crew safely in normal space, unharmed, and nearly ten years closer to home. Janeway orders the crew to dismantle the slipstream technology, believing it not yet ready for safe usage. She later provides Kim with an encoded message found in the signal telemetry: a recording that the future Kim had sent to his past self, giving him much-needed confidence in his abilities.
Credits
Adapted from Wikipedia contributors, Timeless (Star Trek: Voyager). Paragraphs and formatting adjusted; illustrations, reference markers, block quotations and non-story material omitted.