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, though, when he's called to the bridge to help identify an anomaly. It turns out that the anomaly is being 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.
Tom is just finishing repairs on Steth's ship and is preparing to bid the interesting fellow goodbye when Steth grabs him 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 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, who he charms with affection.
Back on Steth's ship, Tom awakens in a new body. He's almost immediately captured by a woman who has a major grievance with Steth (or the alien who had been posing as Steth). It seems that the real Steth is inside the body of female alien named Daelen, and the real Steth wants his body back.
Meanwhile, the alien posing as Tom on Voyager has begun to exhibit behavior that makes the crew suspicious. He is cruel to B'Elanna, starts drinking alcohol on duty, and snoops into Captain Janeway's log. When she demands an explanation for these actions, he jumps her. Tuvok shoots him before he can choke her to death, and she bolts from the room.
Tom has convinced the real Steth that the alien has done both of them wrong, and suggests they join forces to find Voyager and fix the situation. They reach the ship just as the alien flies off with a shuttlecraft, in Captain Janeway's body. Tom disables the shuttle and brings the alien back in. Steth's original body, the one that the alien and Tom had been using, is restored to Steth, and the alien - now trapped back in Daelen's female body - is taken into custody, so all of his/her previous victims can be restored to their original bodies.
Grateful to be back in his own life again, Tom heads off to make up with B'Elanna.