Lili, Vorjak, and the baby flee to find a shuttle to escape Earth. Liam and Sandoval are both tracking them - for different reasons. Augur is on the run from volunteers, but sends a friend (Juliet) to help Liam while he's gone.

Lili, Vorjak, and the baby flee to find a shuttle to escape Earth. Liam and Sandoval are both tracking them - for different reasons. Augur is on the run from volunteers, but sends a friend (Juliet) to help Liam while he's gone.

Lili, Vorjak, and the baby flee to find a shuttle to escape Earth. Liam and Sandoval are both tracking them - for different reasons. Augur is on the run from volunteers, but sends a friend (Juliet) to help Liam while he's gone.

Lili, Vorjak, and the baby flee to find a shuttle to escape Earth. Liam and Sandoval are both tracking them - for different reasons. Augur is on the run from volunteers, but sends a friend (Juliet) to help Liam while he's gone.

三年前，他们来了，永远的改变了人类的未来。他们说他们只为和平而来，称呼自己为“盟友”。各国的领导人欢迎他们的到来，他们帮助解决了我们过去无法解决的难题：战争、饥荒和疾病。他们除了友谊，别无所求。盟友获得了很高的声望和爱戴。他们和世界上的国家，都建立了外交联系。但是这些友善动作的背后，似乎隐藏着什么……

Following Boone's confrontation with Hegel that left him severely injured, he was eliminated by Zo'or. Beckett who was impregnated by Hegel gives birth to a boy who immediately grows up to a man. He assumes the name Liam Kincaid and goes to Boone's funeral where Quon would be eliminated by an alien replicant. After impressing Da'an he is made his new protector.

An unknown woman saves Augur and Liam from the raids on the Resistance. Lili sabotages the mother ship, but Zo'or stops its total destruction. Lili is reportedly dead. The investigation on the President's shooter continues.

Renee has spent company money and time on a search and rescue team to discover what happened to Liam in the chamber. She is asked to cease or quit. She quits, convinced that Liam is alive. Street helps her put together a new search team.

第四季将视野拓展到教育系统，其它主要情节还有第三季中引入的市长竞选，并深入描写了Marlo Stanfield领导的贩毒团伙在西巴尔的摩的不断壮大。