Flash season 4 trailer reveals how Cisco and Caitlin will bring Barry back from Speed Force

The Flash season 4 trailer was unveiled at San Diego Comic-Con and fans finally have an answer to how Barry Allen will return to Central City from Speed Force, following the tragic events in season 3 finale.

The two-minute video opens with scenes from May finale, where the Scarlet Speedster is seen voluntarily walking into the Speed Force. The voice-over opens with Iris West, who seemed shattered, "My name is Iris West and I was supposed to marry the Fastest Man Alive. I promised him I will run, so that's what I have been doing, running as fast as I can."

Then we see Joe asking Iris about how she could she be doing fine but Iris asks "Dad, what do you want me to do? Curl up in a ball and cry all day? Barry is not coming back." She then tells her father that her fiance asked her to be strong and she is doing that.

Later Cisco is seen missing Barry too as he says, "Sometimes I feel like if I believe in something hard enough, that will make it real. I miss my friend." Also, Caitlin, who was seen leaving the Flash team in season 3 finale is back to work in Star Labs.

We also get a glimpse at season 4 villain, who wields a magical sword and claims, "Bring me the Flash or else your city falls." Looks like the new villain's scary warning will force Cisco and team to find a way to bring Barry back.

Cisco is also seen making slight modifications to Captain Cold's gun and is trying to bring back the Speedster with it. We see CGI images of Barry running as Caitlin declares, "I have got a lock on something,"

"It's him," says Cisco and the trailer ends with him blasting the freeze gun.

Grant Gustin, who plays Barry, said that season 4 of The Flash is most similar in tone to the first season of The CW show. He told Digital Spy at Comic-Con, "We've all come really far as actors... so I think we're going to be able to execute everything that we're being given more successfully than we did initially in season one, but it's going to be like that tone of season one."

"We're gonna get that fun, and get back to the comedy of The Flash. It's gonna be great," added the actor. The 4th season will add some new characters to the list including, Ralph Dibny, the Elongated Man, who will be an ally to Team Flash in their battle against new enemy The Thinker ( played by Neil Sandilands).