The Psi Corps and President Clark, whose government has discovered Shadow vessels buried in Earth's solar system, begin to harness the vessels' advanced technology. The Clark administration continues to become increasingly xenophobic and totalitarian, and uses a military incident as an excuse to declare martial law. This triggers a war of independence on Mars, which had long had a strained political relationship with Earth. Babylon 5 also declares independence from Earth, along with several other outlying Earth Alliance colonies. In response, the Earth Alliance attempts to retake Babylon 5 by force, but with the aid of the Minbari, who have allied with the station against the growing Shadow threat, the attack is repelled.
Becoming concerned over the Shadows' growing influence amongst his people, Centauri ambassador Londo Mollari attempts to sever ties with them. Mr. Morden, the Shadows' human representative, tricks him into restoring the partnership by engineering the murder of Mollari's mistress while putting the blame on a rival Centauri House. Open warfare breaks out between the Shadows and the alliance led by Babylon 5 and the Minbari. It is learned that genetic manipulation by the Vorlons is the source of human telepathy, as it is later discovered that Shadow ships are vulnerable to telepathic attacks. Displeased at the Vorlons' lack of direct action against the Shadows, Captain John Sheridan browbeats Vorlon ambassador Kosh Naranek into launching an attack against their mutual enemy. Kosh's deeds lead to his subsequent assassination by the Shadows.
Former station commander Jeffrey Sinclair returns to Babylon 5 to enlist the aid of Captain Sheridan, Delenn, Ivanova and Marcus in stealing the Babylon 4 space station and sending it 1,000 years back in time to use it as a base of operations against the Shadows in the previous Minbari-Shadow war. Undergoing the same transformation as Delenn at the end of Season 1, Sinclair transforms into a Minbari and is subsequently revealed to be the actual Valen of Minbari legend, rather than a reincarnation. Spurred by the reappearance of his assumed-dead wife (who now works for the Shadows), Sheridan travels to Z'ha'dum, the Shadow homeworld, in an attempt by them to recruit him. However he instead destroys their largest city in a kamikaze nuclear attack, and is last seen jumping into a miles-deep pit to escape the explosion. Garibaldi, during a fight with Shadow vessels, goes missing.
萨拉·莫滕森 Sara Mortensen,罗拉·德瓦瑞 Lola Dewaere,米夏埃尔·科恩,卡蜜儿·德·帕兹,布鲁诺·沃尔科维奇,塞尔日·费拉德,萝拉·勒兰恩,范蕾丽尔·卡帕里斯基,丽露·弗格利,奥利维亚·波纳梅,伊凡·弗拉内克,佛洛伦丝·托马辛,菲利普·杜克斯纳,泽维尔·马修,奥利维尔·雷堡汀,尼可拉斯·旺克奇基