Worlds collide when Barry uses his superpowers to travel back in time in order to change the events of the past. But when his attempt to save his family inadvertently alters the future, Barry becomes trapped in a reality in which General Zod has returned, threatening annihilation, and there are no Superheroes to turn to. That is, unless Barry can coax a very different Batman out of retirement and rescue an imprisoned Kryptonian, albeit not the one...

Relegated to Hollow Earth, Kong feels lonely and continues to search for his family, but instead finds a fearsome enemy imprisoned and on the verge of breaking out to conquer the humans. Alongside his human family -- Jia, Ilene, Trapper, and Bernie -- he ventures above ground to recruit help from Godzilla and other Titans, but making allies from old enemies is never easy!

Soon after Emma and Hook unwittingly bring Elsa of Arendelle to Storybrooke, they encounter the mysterious "Snow Queen," whose relentless obsession with both Emma and Elsa has chilling consequences. Meanwhile, it appears Regina has at last found true love with Robin Hood, but how will she react when her happy ending is thwarted yet again by a maddening, seemingly pre-ordained twist of fate?

After a Black Friday riot ends in tragedy, a mysterious Thanksgiving-inspired killer terrorizes Plymouth, Massachusetts, the birthplace of the infamous holiday.