The crew is haunted by memories of a massacre.
After a two-week away mission, Chakotay, Tom Paris, Harry Kim and Neelix begin having vivid visions of fighting in a war, and Neelix even takes Naomi Wildman hostage during one episode. The memories show them as soldiers evacuating a colony of Nakan civilians, an operation that turned into a massacre in which dozens of colonists died, while their commander destroyed the bodies to hide what happened. Soon Janeway and other crew members share the visions.
Voyager returns to the planet and finds the remains of two victims, but they are three centuries old. The source is a monument that sends the memories of the massacre into the minds of anyone nearby, so it can never be forgotten. Tuvok wants it shut down, but Neelix argues that the dead deserve to be remembered, and Janeway repairs it and leaves a warning buoy. The sixth-season episode deals with war crimes and the duty to remember them.