While escorting the retired USS Voyager to Earth, the crew battles a revived macrovirus, and a transporter accident fuses T'Ana and Billups into one being.
The Cerritos escorts the decommissioned USS Voyager to Earth, where it is to become a museum. A dormant macrovirus from the Delta Quadrant awakens and overruns Voyager, and Boimler, anxious about an upcoming promotion, enlists Rutherford's help to stop it.
On the Cerritos, a Delta Quadrant flower causes a transporter accident that merges Dr. T'Ana and chief engineer Billups into a single being, T'illups. Remembering what happened to Tuvix aboard Voyager, T'illups fears being separated and starts fusing other crew members. Tendi and T'Lyn combine everyone affected into one mass and then pull them apart. Boimler, Tendi, T'Lyn and Mariner are promoted to lieutenant junior grade, and the Klingon ship Che'Ta is attacked by a mysterious vessel.