Tom Paris has become restless and uninspired by life on Voyager. Lately he's been spending a lot of time in a holodeck program restoring a 1969 Camaro. He hasn't been paying much attention to his girlfriend B'Elanna Torres and he's been skipping out on his shifts in Sickbay as The Doctor's assistant.

His attention is sparked when he is called to the bridge to help identify an anomaly, which turns out to be caused by a ship with a working coaxial warp drive, a technology previously thought to be only hypothetical.

A vessel equipped with such a system would be able to leap great distances almost instantaneously. The ship is malfunctioning and the crew of Voyager welcomes the pilot on board and offers to help fix his fascinating ship. Tom Paris is the first to volunteer.

The pilot, Steth (Dan Butler), is an adventurer of sorts making a living as a test pilot taking new ship designs out on their first flights. Tom and Steth become fast friends, and Tom requests time off from his boring Sickbay job to help figure out Steth's flashy new ship. Steth invites Tom on a road trip, offering him a chance to fly new kinds of vessels and see the sights, but when he considers his obligations on Voyager, Tom regretfully declines.

After completing the repairs on Steth's ship and is preparing to bid him goodbye, Steth grabs Paris and somehow switches bodies with him. Steth has lost his ability to keep his consciousness and body combined, and must take a new body. Steth remains on Voyager in the body of Tom Paris, and sends his ship, and Tom's mind, away at high speed.

Safely hidden behind Tom's friendly face, Steth assumes a new life. He has none of Tom's memories and has a different personality, so fitting into the crew proves to be challenging. This new Tom Paris confounds the Doctor, whom he flatters into giving him a vacation, and B'Elanna, whom he charms with affection.

Back on Steth's ship, Tom awakens in a new body. He is almost immediately captured by a woman who has a major grievance with Steth (or the alien who had been posing as Steth). It seems the real Steth is inside a woman's body, an alien named Daelen, and the real Steth wants his body back.

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Wikipedia