The I-400 saga comes to a conclusion in the edge of your seat midseason finale!

Thanks to their new ally, I-402, the crew of the Missouri know of I-400's plan to bring about galactic extinction, which involves flying Planetoid Lazzaro, a sparsely populated Class L planetoid from the Romulan Neutral Zone, into the Great Barrier at the Galactic Core and detonating the dilithium payload I-400 has embedded into the planetoid's crust, creating an energy wave of Great Barrier energy which would wipe out all life in the galaxy.

Intent on not letting that happen, Commander Cooke is authorized to lead a Starfleet task group to organize an evacuation of the planetoid. However, the Federation is not the only galactic power that I-402 has alerted, for when Starfleet arrives, they find a flotilla of ships from the Romulan Star Empire, Klingon Empire, Cardassian Union, and even the isolationist Breen Confederacy on scene, with Dominion vessels en route from the Gamma Quadrant. It seems that all the major galactic powers are setting aside their differences in the name of preserving life in the galaxy, and the stage is set for the ultimate showdown between this hastily thrown together galactic alliance and the entirety of I-400's forces.

When the dust settles, Commander Cooke is promoted to Captain, and the Missouri, still bearing the scars of battle, is formally christened.