Conflict between two species who petition for membership in the Federation turns out to be the B-plot. On its way past a mysterious optical special effect, the Enterprise picks up a strange glowing spark via the sensor array, and as such entities tend to do in Star Trek, it starts wreaking havoc. We get a lot of exterior shots of the ship, some alien character designs that would have worked better in background shots, a glimpse at a sensor relay room we’ve never seen before (though it’s pretty obviously a redress of Engineering), and some glimpses of the Crushers at home.