The Borg show up, jumping up and down lightly on continuity.
There’s a great episode of the Doctor Who reboot, Dalek, that manages to take back a villain that had become so overused we’d forgotten the menace. This episode is not as good, but it still reminds us of just how significant the Borg threat is. Two Borg can start an invasion, take over a ship, generally ruin your whole day.
The back half turns into an action sequence with a few plot holes (why exactly were the invading Borg beamed back to the soon-to-be-destroyed ship?) that’s fun without being tremendously deep.
(On the continuity thing: there’s a bit of contortion to avoid saying ‘Borg’, but they do make it plausible. To be honest, it was First Contact that created the real continuity problem).
Callbacks: The Borg. Duh. But most especially, the start of the Borg invasion is here, with the transmission to the Delta quadrant.
687 down, 50 to go.