'Legends of Tomorrow' season 2 episode 7 spoilers: Time aberration threatens Professor Stein's memories

The highly anticipated four-way crossover between The CW's superhero shows are about to kick off next week and its heart-pounding conclusion lands on the next episode of "Legends of Tomorrow."

At the end of episode 6, newly appointed team captain Sara Lance (Caity Lotz) told her team that she just received an SOS from their friends back in 2016, thereby hinting at the arrival of the biggest menace to ever threaten executive producer Greg Berlanti's DC universe.

The annual crossover event begins in "Supergirl," which joined The CW's superhero lineup this year, when Barry Allen/The Flash (Grant Gustin) and Cisco Ramon (Carlos Valdes) create a breach between parallel universes to reach out to Kara Danvers/Supergirl (Melissa Benoist) for help. It will later be revealed that Barry's team has also brought in Oliver Queen, aka The Green Arrow (Stephen Amell) and his most trusted allies, along with the whole Legends of Tomorrow crew, as shown in the brief crossover trailer released by The CW.

According to the official press release for the episode titled "Invasion!," when the crossover event finally reaches "Legends of Tomorrow", the gang of superheroes will have already figured out what their adversary, the Dominators, plan to do. No details have been revealed about this yet, but based on the "Invasion!" storyline in the comic books, there have been speculations that this menacing alien race could be after Earth's superheroes and metahumans for experimentation purposes. They may threaten to destroy a huge portion of Earth and demand humanity to surrender their superheroes for the sake of the majority.

But while Martin Stein (Victor Garber) comes up with a plan to terminate the Dominators, he himself is threatened by an aberration he unknowingly created when they went back to 1987. Will the band of superheroes defeat their enemies before it's too late? Will Stein be able to regain the memories that he is gradually losing, and could his condition affect their plans in a major way?

The crossover starts next week in "Supegirl" on Monday, Nov. 28 and continues in "The Flash" on Tuesday, Nov. 29, "Arrow" on Wednesday, Nov. 30, and finally concludes in "Legends of Tomorrow" on Thursday, Dec. 1. All shows air at 8 p.m. EST on The CW.