The Fall of Night is the final episode of the second season of Babylon 5. Set at the end of 2259, it reveals the increasing hold the paramilitary thought police known as the Nightwatch has on Earth and some of the station's human personnel. It is also a benchmark in the Centauri-Narn war and foreshadows a change in the "official" status of Babylon 5.
A Narn warcruiser appears from a jumpgate near Babylon 5 just after the arrival of diplomatic personnel from Earth. The warcruiser was away from the Narn homeworld at the time of its invasion by the Centauri, and its captain petitions Captain Sheridan for time to make repairs and be safe from attack under Babylon 5's protection. He keeps their location secret, revealing it only to command personnel and Narn Ambassador G'Kar.
However, one of the diplomats, Mr. Wells, is actually a Nightwatch organizer and attempts to recruit Commander Ivanova. This fails, although Wells encourages the station personnel -- some security, some command and control -- who have joined the Nightwatch to be more vigilant in reporting suspicious or "disloyal" activity. The senior diplomat reveals to Sheridan that Earth has signed a non-aggression pact with the Centauri, whom Sheridan's crew already knows is responsible for instigating the latest aggression against the Narn. But officially Earth is more concerned with peace.
The Centauri send a warship to Babylon 5 and through Ambassador Mollari demand to seize the Narn warcruiser and its crew. Sheridan dispatches Zeta Squadron to protect the Narn when they pass through the jumpgate as the Centauri warship fires on them and Babylon 5. Only after they've been fired upon do they attack the Centauri warship and destroy it.
While passing through hyperspace, the leader of Zeta Squadron detects the elevated neutrino emission that comes from a Shadow vessel and follows it. Back on the station, Sheridan is on his way to a diplomatic apology he is to give the Centauri in the Zen garden. But a bomb set by a Centauri goes off on the public transport he's using to get there and he enters freefall high above the garden itself. Vorlon Ambassador Kosh Naranek reveals his true form as an angel-like being represented in every culture as a deity and rises to save Sheridan's life. Across the station, individuals share this story and each claim to have seen their respective god, all but Londo, who says he saw nothing.
The episode ends with foreshadowing by Commander Ivanova. The Nightwatch cracks down on disloyalty they see evidenced on Babylon 5, and the Centauri become more aggressive by the day.
