Cassandra Spender: I told you that the aliens were here to do good... Only now I know what the aliens are here for - and it isn't good.

Mulder: What are they here for?

Cassandra Spender: To wipe us off the planet.

Mulder and Scully return from Antarctica to discover they've been reassigned and are no longer a part of The X-Files. Their frustration turns to fear when Cassandra Spender, a woman who claims to have been abducted the same night as Mulder's sister, reappears with claims of an alien threat. But it is an extraterrestrial artefact found off the coast of Africa which may hold the key to the very origins of life on Earth and which has an unexplained and deadly effect on Mulder.