The Flash 3×20 “I Know Who You Are” Season 3 Episode 20 Extended Promo – VIBE FACES OFF AGAINST KILLER FROST – Barry (Grant Gustin) and the team meet Tracy Brand (guest star Anne Dudek), a scientist, who may be the key to stopping Savitar. Unfortunately, Killer Frost (Danielle Panabaker) is also after Tracy so Team Flash must battle their old friend, which proves to be particularly difficult for Cisco (Carlos Valdes). Joe (Jesse L. Martin) and Cecile’s (guest star Danielle Nicolet) relationship takes a big turn. Hanelle Culpepper directed the episode written by Bronwen Clark & Joshua V. Gilbert (#320). Original airdate 5/2/2017.