With a larger role in Season 4, take a look @ footage, images and synopsis from Season 3 of "The Flash" episode "Killer Frost", written by Judalina Neira, Andrew Kreisberg, Brooke Roberts and directed by Kevin Smith, that aired November 22, 2016 on The CW:
"...'Caitlin' (Danielle Panabaker) uses her powers to save 'Barry' (Grant Gustin) but as her mother predicted, the effort unleashes her inner 'Killer Frost'.
"Killer Frost goes on a rampage looking for 'Dr. Alchemy', kidnapping 'Julian' (Tom Felton) and battling both 'The Flash' and 'Vibe' (Carlos Valdes). Meanwhile, 'Joe' (Jesse L. Martin) and 'H.R.' (Tom Cavanagh) have a heart to heart talk..."
Click the images to enlarge and Sneak Peek "The Flash: Killer Frost"...