Tom uses a shuttle to travel to warp ten. Once he reaches the threshold he's everywhere at the same time, becomes Kwisatz Haderach. When he comes back he starts mutating, loses his mind, kidnaps the captain, they fly off at warp 10.

By the time voyager finds them they've devolved(or evolved) into small amphibians, luckily the doc has a magic serum that will fix them. As the crew are about to leave they notice a bunch of tadpoles escape from the nest. Basically Tom and Kat had tadpole babies.