Lt. Barclay - the notorious engineer from "Next Generation" claims to have figured out a way to contact Voyager by the means of a wormhole. Unfortunately nobody believes him because of his previous mental conditions and his obviously obsessive behavior. So with some moral support from his friend/shrink Diana Troy (also known from "Next Generation") he takes fate in his own hands.
In my opinion one of the best episodes on Voyager. Although I admit it's probably influenced by my infatuation with "Next Generation". Somebody who wasn't an fan of NG could very well argue, that the regulars of Voyager are underrepresented in this episode.