Mariner's feeling a bit sour because she and the lower decks gang go left out in space for six hours when the Cerritos has to warp away to help another ship in trouble. Also, a Starfleet drill instructor is showing up to run the entire crew through performance reviews and Captain Freeman wants everybody to be at their best. When the drills involve the lower decks folks assuming senior staff positions (and the senior staff being lower decks), the event become a chance for Mariner et al to show just how well they would do if they were charge.
Nothing goes wrong, of course.
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