In season 4, an unknown force is destroying starships and threatening galactic peace. Luckily, the crew of the U.S.S. Cerritos isn't important enough for stuff like that! Instead, Ensigns Mariner, Boimler, Tendi, Rutherford and Provisional Ensign T'Lyn are keeping up with their Starfleet duties, avoiding malevolent computers and getting stuck in a couple caves β all while encountering new and classic aliens along the way.

The Cerritos ensigns must assist a caretaker on the voyage of a historically significant starship.

Mariner tries to get demoted, Rutherford tries to get promoted, and Boimler makes a big move.

Boimler leads his first away mission on an alien megastructure.

Tendi is summoned back to Orion for a wedding.

A trio of Betazoids cause chaos on the Cerritos.

The Cerritos visits the Ferengi homeworld.

Three computerized villains return to cause problems for the Cerritos crew.

The Lower Deckers go on a classic cave mission.

Captain Freeman assigns the Lower Deckers an overly safe mission to try and keep a self-destructive Mariner out of danger.

Mariner faces her past in the season four finale.