This week's episode of The Flash
, entitled "The Nuclear Man", marks the return of Firestorm, the villainous combination of Ronnie Raymond
) and Martin Stein (Victor Garber
). Today, The CW released a brief preview of tomorrow night's episode, where executive producer Andrew Kreisberg
explains that fans will finally learn what exactly happened that lead to Firestorm's creation. As you may recall, Ronnie, the fiancee of Caitlin Snow (Danielle Panabaker
), vaporized during the show's third episode, and the mystery behind how Robbie and Martin became Firestorm will be solved.
After Ronnie (guest star Robbie Amell
) attacks a physicist (guest star Bill Dow
), Barry and the team realize they need to go after Caitlin's (Danielle Panabaker
) fiancé who is now a dangerous meta-human. They deduce the best way to track Ronnie is to find Dr. Martin Stein (guest star Victor Garber
) who was working on a project called F.I.R.