Zack finally locates Garibaldi. Delenn faces opposition from the League of Non-Aligned Worlds in organizing a strike against the Shadows. Sheridan returns from Z'ha'dum, to the shock of everyone aboard the station. The joy of reunion is, however, quickly overshadowed by the report of the vast Vorlon fleet that has just destroyed Arcata 7, an inhabited planet of millions of sentients, because it had harbored a Shadow force. The Vorlons have decided that it's time to destroy everything that has been touched by the Shadows. Now the Army of Light must stop both the Shadows and the Vorlons if anyone hopes to survive this struggle.
Sheridan returns, alive, and rallies the Non-Aligned worlds against the Shadows.
Ivanova discovers a "pocket" in hyperspace being used by the Vorlons to hide their massive armada, replete with Star Dreadnoughts, Fighters, and their most powerful weapon, the Vorlon Planet Killer. Soon after, the Vorlons obliterate a planet in league with the Shadows.
Initially, when the Vorlons and Shadows took on the task of looking after the younger races, they were equally balanced, obeyed rules of engagement, and respected each other's perspectives. But at some point, one of them grew tired of the arrangement and the two started fighting in earnest, with the younger races caught in the middle.
Lyta's telepathic abilities were enhanced by the Vorlons to enable her to more easily carry one of them.
The Vorlons, apparently determined to wipe the Shadows out once and for all, have begun destroying worlds that have had contact with the Shadows, and to that end have amassed a fleet of thousands of ships, as well as the Planet Killer.