Barry and Caitlin must navigate their relationshiop after revelations are made amidst a new serial killer in 'The Black Flame' striking Central City.

As Barry has a moment of introspection, he finds something he always knew, but is too scared to act on it, and the arrival of a mysterious alien with tales of Armageddon send Barry spiraling, and only one woman can pull him back from the brink of insanity. Snowbarry.