犯罪心理研究小组隶属FBI，他们跨州行动，主要针对连环杀人案，从嫌疑人的犯罪心理和行为模式入手建立人物侧写，圈定罪犯的性别、年龄、职业特征、居住环境乃至成长经历，从而预测罪犯下一步行为，直至缉拿罪犯。他们的成员包括：高智商、强记忆力的少年天才斯拜瑟尔·瑞德博士（马修·格雷·古柏勒 Matthew Gray Gubler 饰）——负责数据和资料分析；外冷内热的硬汉阿伦·哈奇（托马斯·吉布森 Thomas Gibson 饰）——沟通能力极强，波多黎各小伙德里克·摩根（谢默·摩尔 Shemar Moore 饰）——强制性犯罪行为专家；打扮招摇的小胖妹佩妮洛普·格西娅（克里斯汀·范奈丝 Kirsten Vangsness 饰）——数据库专家，美女媒体联络员JJ（A·J·库克 A.J. Cook 饰）等，在老探员戴维·罗西（乔·曼特纳 Joe Mantegna 饰）带领下，飞往全美各地，展开一场场缉凶行动。
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.
