The mythology arc spins up in a big way with Two Fathers. Written by series creator Chris Carter and Frank Spotnitz, the episode first debuted on 7 February, 1999, and sees the return of Cassandra Spender (Veronica Cartwright), the reveal to Mulder (David Duchovny), Scully (Gillian Anderson) and Skinner (Mitch Pileggi) that CSM (William B. Davis) is Cassandra’s ex-husband, and Agent Jeffrey Spender’s (Chris Owens) father.

And that’s just the tip of the iceberg as Cassandra is discovered in a familiar looking operating room in a train car, but those who were working on her were all burned alive by the alien rebels. Apparently the rebels are trying to force the Syndicate out into the open so that they will be forced to join forces with the rebels against the alien invasion.

The Syndicate has been collaborating with the invasion in a time to buy time to create their human/alien hybrid that would allow the species to survive the viral outbreak that would garner instantaneous repopulation as seen in Fight the Future. Humanity would survive but we would be a slave race, but the Syndicate may retain some power.

Mulder despite being ousted from the files is summoned by Cassandra who reveals as much to the two agents as she knows her own son won’t believe her. The duo are able to tie all of the threads together, including the involvement of Mulder’s father (Peter Donat) and the abduction of his sister.

Meanwhile, Spender seeks out CSM but when he’s given an assignment to off a rebel, disguised as a Syndicate member, Krycek (Nicholas Lea) reveals what is really going on to the agent. And all through the episode, CSM is relating information to someone, and as we race to a cliffhanger that sees Cassandra asking Mulder to kill her, she knows she’s the key to the alien/human hybrid problem, it’s revealed that CSM has a new ally, and its hinted just a little more, in Agent Diana Fowley (Mimi Rogers).

The cliffhanger was resolved a week later on 14 February, 1999 with One Son, also written by Carter and Spotnitz. Picking up moments after the previous episode, Mulder’s door bursts in, and Fowley along with a team from the CDC lock down his apartment, and take Cassandra into custody, and while Mulder is happy to see Fowley, Scully still doesn’t trust the agent.

And she’s right to, despite Mulder’s seemingly blind trust in her, Fowley is working with CSM, and working to further the project put forward by The Syndicate. While Mulder and Scully are being held in a facility, where he discovers Marita Covarrubias (Laurie Holden), the Syndicate moves forward with its readiness for colonisation, with Cassandra in their hands.

Unfortunately, the rebels are still working to get humanity’s resistance in the open, by drawing The Syndicate into a trap, that may cost a number of lives, though a few villains escape.

Like the previous episode, there is a lot of exposition in the form of dialogue, which sees a confrontation between CSM and Mulder, who gives the FBI agent a little bit to think about when he tells the story from the other perspective. How much of it is lies, how much of it can be changed, what does the future offer?

After the events at the climax of the episode, Agent Spender tenders his resignation to Kersh (James Pickens Jr.) advising him that there are two agents who should be running the x-files, and could have served better…

Looks like Mulder and Scully are back in their offices (though there may be a mess to clean up following a final visit between Spender and CSM). And that’s a good thing, because the truth is (still) out there.