Janeway and Seven try to stop a dangerous particle.
Voyager discovers traces of Omega, a molecule that Starfleet regards as so dangerous that its destruction takes priority over almost any other mission. Janeway invokes a secret directive, and Seven of Nine reveals that the Borg are also interested in the substance.
The episode shows the crew facing a threat that Starfleet treats as a top priority, and it forces Janeway to weigh orders against the wishes of her people. It is also a character story for Seven of Nine, who finds a rare moment of perfection in the experience.