The episode also marks an important turning point among the series when Janeway notes in her personal log the changing perspective of their journey home: it's no longer "if" the crew will ever return to Earth, but "when."

The episode begins with a "cold opening" on a frigid windswept planet. Two figures wearing survival gear beam onto the scene and search until they discover what they are looking for: Voyager, buried beneath the ice.

Fifteen years in the future, Chakotay and Kim discover Voyager frozen on the surface of an ice world. They recover the body of Seven of Nine and collect the Doctor via his mobile emitter, and return to the Delta Flyer, joining Tessa Omond (Christine Harnos). Kim restores the Doctor and explains that fifteen years prior, the crew had attempted to use the slipstream engine technology to bring Voyager home, with Chakotay and Kim in the Delta Flyer leading the larger ship. However, the slipstream became unstable due to a phase variance, causing Voyager to fall out of the slipstream and crash into the ice world, its position in the Alpha Quadrant lost. Chakotay and Kim have spent the last nine years, after Starfleet called off the search, looking for Voyager. Kim explains that he can send a message back in time to Seven via her interplexing beacon using a stolen Borg temporal transmitter, which would then prevent the accident, allowing Voyager to have arrived home safely. They brought aboard the Doctor to help extract the chronometric node from Seven and identify the exact time when her cybernetic systems disengaged as to know when to send the corrections.

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Wikipedia