The highly-anticipated superhero crossover will finally happen in the upcoming episode of "Supergirl" season 2.

In the episode titled "Medusa," Team Flash's Barry Allen (Grant Gustin) and Cisco Ramon (Carlos Valdes) of "The Flash" will drop by from Central City to ask Kara (Melissa Benoist) to help them prevent an alien invasion on their Earth.

This is not the first time that Barry, also known as The Flash, visited National City to contain the threat in the city caused by Livewire (Brit Morgan) in the first season of "Supergirl." The two had a great working relationship together, which could possibly repeat again this season.

However, Kara will also have a problem of her own after CADMUS dropped a deadly virus that could affect and kill all the alien species in the vicinity. Kara must act fast in order to fix this, so she must seek the help of an unlikely allied to stop the virus. This means that Kara must work with Lena Luthor (Katie McGrath) to be able to succeed in this mission.

On the other hand, the episode will also feature the reunion between the Danvers ladies for Thanksgiving. This will prompt Kara's sister, Alex (Chyler Leigh), to open up to their mother, Eliza (Helen Slater). The two already has a complicated relationship for a while, and the truth that Alex had been hiding from her mother could make it worse.

Elsewhere in the episode, Eliza will shock Kara when she declared that Mon-El (Chris Wood) has feelings for her.

The eighth episode of "Supergirl" season 2 will air on Monday, Nov. 28. But the four-night crossover episodes of the other DC Comics-inspired series will continue until the next episode of "The Flash" season 3 on Tuesday, Nov. 29, "Arrow" season 5 on Wednesday, Nov. 30, until the final installment on Thursday in "DC's Legends of Tomorrow" season 2.