In the scene, Barry Allen meets Professor Martin Stein on a train -- perhaps on his way back from Starling City, since this is the day of the particle accelerator accident at S.T.A.R. Labs. And it isn't without a little humor...or foreshadowing.
You can check it out, along with the official synopsis for the episode, below.
“The Nuclear Man” — (8:00-9:00 p.m. ET) (TV-PG, DV) (HDTV)
ROBBIE AMELL AND VICTOR GARBER GUEST STAR AS FIRESTORM; After Ronnie (guest star Robbie Amell) attacks a physicist (guest star Bill Dow), Barry (Grant Gustin) 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.E.S.T.O.R.M. Barry struggles to balance his duties as The Flash and his relationship with Linda Park (guest star Malese Jow), and Joe (Jesse L. Martin) enlists Cisco’s (Carlos Valdes) help to reinvestigate the murder of Nora Allen (guest star Michelle Harrison). General Eiling (Clancy Brown) returns to Central City. Glen Winter directed the episode written by Andrew Kreisberg & Katherine Walczak (#113). Original airdate 2/10/2015.
The Flash airs Tuesday nights at 8 p.m. ET/PT. "The Nuclear Man" episode premieres tonight.