A small experimental ship with a coaxial warp drive, flown by the body-stealing alien who called himself Steth when he met Voyager in 2374.
Steth's ship appears in the Voyager episode Vis à Vis. Voyager finds it in trouble: its coaxial warp drive, which folds space so that a ship can cross great distances almost at once, is unstable and close to exploding.
Tom Paris, bored with routine, throws himself into helping the pilot repair it and solves the problem with an idea borrowed from old Earth car engines. The pilot is not who he seems. He is a thief who swaps bodies with his victims, and he takes Paris's form and place aboard Voyager.
Paris wakes in Steth's body aboard the coaxial ship, far from Voyager. With the help of the real Steth, an earlier victim, he gets back and the exchanges are undone.