One of the bigger ongoing mysteries in The Flash has been solved, as this week's episode revealed the origin of Caitlin Snow's Killer Frost powers. Warning: this article contains spoilers for "The Icicle Cometh"! Last season, viewers learned that Caitlin originally manifested her Killer Frost powers as a child, contradicting the belief that she had been transformed by the STAR Labs particle accelerator explosion like most of Central City's metahumans.