A Flash of the Lightning

Synopsis
Faced with the news of his impending death, Barry’s resiliency suffers as he struggles to fight fate. Meanwhile, Cecile’s career as a D.A. conflicts with her identity when she crosses paths with a villainous meta-human.

Trivia

 * The episode shares its title with Crisis on Infinite Earths eponymous eighth issue, which featured Barry sacrificing himself to save the multiverse.
 * The episode itself makes use of the title in the poem read by Joan Williams in an attempt to bring Barry back to consciousness.
 * Jay tells Barry that he had spent a year tracking the spread of antimatter throughout the multiverse, showcasing a map of the Earths he had discovered thus far. The map featured annotations from Jay, which ranged from the Earths that have the best vegan food and tequila, to which superheroes call which Earth home. Towards the top of the list, next to the Earths 52, 4, and 260, presumably on Earth 51 (his home Earth in the comics), is the name "Thaddeus Brown". In the comics, Thaddeus was the first to hold the mantle of Mister Miracle.
 * Also on his map, Jay predicts that the antimatter wave would next appear on Earth-2. This was seen in Arrow's episode "Starling City," which aired directly after this one.
 * This is the first episode where Killer Frost appears throughout the entire episode instead of Caitlin.
 * In the recovery bed, Barry tells Joan that she should have used Lady Gaga to reawaken him. This is a reference to, where Caitlin and Cisco played a Lady Gaga song when Barry woke up from his coma.
 * The man who saved Esperanza was wearing the logo of the Black Hole organization from the comics which was connected to Godspeed
 * In the comics, which lasted across three issues of Titans in 2010 and 2011. Allegra Garcia was the daughter of the villain Eduardo Reyes/Wavelength. Initially born in the Amazon and raised in the slums of Brazil by adopted parents, Allegra inherited her father's abilities to control electromagnetic light. After she was sentenced to Arkham, Deathstroke and his Titans team were sent to rescue her, and led to a fight between Deathstroke and Batman. Ultimately, Allegra was rescued and returned to Brazil, only to quickly kill her birth father, which led to Slade putting a power-dampening collar on her.
 * Barry's vision shows Cisco suited up in his Vibe suit again, hinting that he'll somehow regain his powers.
 * Nanites, courtesy of Ray Palmer are used to help Killer Frost blend in.
 * Cisco calls Killer Frost a White Walker, referencing Game of Thrones.