Voyager discovers an injured Hirogen who is in the middle of an intense hunt for what is a formidable and dangerous prey even for Hirogen standards. He is brought in to sickbay for treatment, but is eager to get back out and track down his trophy prey. Before he is able to do so, the prey alien invades Voyager. It is a tough, armored, telepathic, insectlike creature that the Borg have designated Species 8472.
When the Hirogen targets the 8472, the latter telepathically communicates with Tuvok, pleading to be rescued from the hunter and returned to its home, which is a different dimension known as "fluidic space." Captain Janeway immediately asks Seven of Nine to help the alien return to its home territory. Seven refuses. Species 8472 is so powerful that it can destroy the Borg, and Seven's loathing of the species is still deeply ingrained.
The Hirogen escapes his confines and corners 8472. He grapples with it and Seven beams both of them to one of the Hirogen ships nearby. By allowing the Hirogen to capture 8472, Seven has blatantly disobeyed Janeway, and she is disciplined with limits on her access privileges.