Threshold

Voyager's engineers find a way to use a newly discovered form of dilithium to break the warp 10 barrier, a feat that could bring the ship home almost at once. Tom Paris volunteers to pilot the modified shuttle Cochrane, accepting the risk, and succeeds, reporting that for a moment he was everywhere in the universe at the same time. Back aboard, he begins to change: he becomes allergic to water, can no longer breathe oxygen and turns increasingly hostile, as the Doctor discovers that his body is mutating at an alarming rate. Before he can be treated, Paris escapes from sickbay, kidnaps Janeway and takes the shuttle back to transwarp. After three days of searching, Chakotay and Tuvok find the Cochrane on a swampy planet, where Paris and Janeway have both transformed into amphibious creatures and produced three offspring. The pair are brought back to Voyager and restored by the Doctor, and the offspring are left behind on the planet.