'Orphan Black' season 4 episode 9 spoilers: Sarah and Rachel work together to defeat a common foe, Helena returns after short hiatus

This week's penultimate episode of hit science fiction series "Orphan Black" season 4 will feature Sarah as she joins forces with Rachel to put an end to their common enemy.

According to the official synopsis for episode 9 titled "The Mitigation of Competition," the story will pick up on the events after Susan Duncan was deposed. Under the management of a new HBIC, Sarah finds herself in a similar situation with Rachel. A common foe will eventually bring them together, which leads to the archenemies cooperating with each other for the greater good. The two will stop at nothing just to finally put an end to Evie Cho & Neolution once and for all.

Meanwhile, Cosima and Susan are still continuing their research to find a cure. The two are at odds since they can't agree on the ethical consequences brought about by experimenting on human subjects. Elsewhere, the Hendrixes' legal counsel, Adele, begins to probe Donnie's case to look for more details. She later on suspects that Felix may be hiding something from her. The episode will also see the much-anticipated return of Helena after being on a short hiatus. her comeback forces Felix to make a very tough decision.

With the show only one week away from its season 4 finale, fans may be wondering if the show will be renewed for another season. As of now, the network has yet to announce further details about a possible season 5. In an interview with E! News back in April 2015, series co-creator John Fawcett mentioned that they plan to conclude the show after the fifth season.

Catch all-new episodes of "Orphan Black" season 4 which airs Thursday nights at 10 p.m. EST on BBC America. The promo clip for this week's episode can be viewed here.