Of its passengers, Tuvok has minor injuries but Chakotay is diagnosed as brain dead. Logs show that during an encounter with a black nebula, all of Chakotay's neural energy was depleted and would cause his death if not replenished quickly. While Voyager returns to the nebula, B'Elanna places Chakotay's medicine wheel above him as he had
                                            requested.

Oddly, several inexplicable events begin unfolding: Paris locks helm control out and changes course twice, while B'Elanna shuts down the warp core. Kes announces she can sense an alien presence that may be possessing the officers, and is soon found unconscious with Tuvok in a turbolift. Because they deduce the alien can control different people at different times, Janeway transfers all command codes to the Doctor, but even he is soon found deactivated.

As the ship returns to the nebula, Janeway discovers that the alien has taken over Tuvok, who takes command of the ship. Suddenly they realize another essence is at play: it's Chakotay, who had been trying to help all along. He signals the correct path out of the nebula with a pattern in the stones on his medicine wheel, and soon is revived while the alien in Tuvok is
                                            released.