"Renaissance Man" is the 170th episode of Star Trek: Voyager, and the last standard-length episode of the seventh season (and series). The succeeding episode, "Endgame", is a double-length episode and the series finale.

En route from a medical conference back to Voyager, the Delta Flyer carrying Captain Janeway and the holographic Doctor is captured by Zet and Nar, members of the Hierarchy. They keep Janeway in captivity and force the Doctor to return to Voyager using disguises enabled by his holo-emitter to get the crew to turn over the warp core and several gel-paks. Zet inserts programming into the Doctor's program to allow them to directly monitor and communicate with him. As the Doctor leaves, Janeway begins to talk with Nar in secret away from Zet, hoping to gain his trust.

The Doctor, disguised as Janeway, returns along in the Delta Flyer and creates a fake transmission from a race called the R'Kaal; the R'Kaal transmission describes the area of space they are in as highly unstable to warp fields, and demand Voyager turn over the warp core, while allowing the crew to settle on a nearby class-M planet. The Doctor — as Janeway — has the Delta Flyer modified to be able to tractor the warp core away should it become unstable. The crew are uneasy at Janeway's willingness to give over the core so easily, forcing the Doctor to try to hide his tracks, including sedating Chakotay and Kim when they come too close to discovering his identity.

Eventually, Tuvok succeeds in discovering the Doctor's deception, and goes to the Sick Bay to stop him. They find the Doctor listening to "The Blue Danube", which the Doctor has been using to mask his communications to Zet from the ship's internal sensors. The Doctor flees via hologram, triggers the ejection of the warp core, and escapes with it via the modified Delta Flyer, leaving no trail that the crew can follow. Shortly afterwards, all the computer systems across the ship begin playing "The Blue Danube", and Seven of Nine recognizes that some of the notes are not correct. They discover the Doctor secretly left a coded message within the recording, and use it to find a warp signature that they can trace. Tuvok and Paris leave in a separate shuttle to follow it.

The Doctor returns to the Hierarchy fleet, and is recaptured despite Janeway's orders to not give over the warp core. With the mission considered a success, Zet decides to use the Doctor to similarly infiltrate the Hierarchy's command structure as to gain valuable information and begins to program the Doctor with a Hierarchy holo-profile; the nature of the profile causes the Doctor's matrix to begin to destabilize. Just then, Tuvok and Paris arrive and begin firing on Zet's ship. Zet ejects the warp core with the intent of destroying it, taking out several of the nearby ships as well as the Voyager shuttle, but the Doctor struggles with Zet to prevent him from firing upon it. Zet orders Nar to help him fend off the Doctor but Nar, now seeing Zet's recklessness, helps the Doctor to subdue Zet.

...
Wikipedia