Season 4 of The Flash is set for Oct. 10, and the cliffhanger ending of the third season finale, "Finish Line," left viewers with lots of questions about Barry Allen's future, as well as that of Team Flash. The season-long effort to defeat Savitar and stop him from murdering Iris West came at the cost of H.R. Wells's life. Worse, a massive Speed Force storm swirled across Central City, threatening to break it apart. This led Barry to atone for the upheavals he caused by reentering the Speed Force.

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Although he was accompanied by a vision of his mother, who made it seem that this would be a positive thing, all the people in his orbit -- Iris, her father Joe, buddy Cisco Ramon and the others -- were left stunned and in despair. SO where will things go from there? Some things about the new season we already know, but the circumstances around the show still open many avenues that it can take in the episodes ahead. Let's explore those possibilities together, in a list of things we already know and what we hope is actually true!

15 KNOW: SIX MONTHS LATER ...

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When Season 4 opens, Barry Allen (Grant Gustin) has been in the Speed Force for six months. How does Team Flash cope with his imprisonment? It must hit hardest for Iris West (Candice Patton) who had their happy ending taken away at the last moment, and Joe West (Jesse L. Martin), losing his son.

The Flash Season 4 trailer, released on July 22 at the San Diego Comic-Con, gave some clues. We certainly can expect that best friend Cisco Ramon (Carlos Valdes) has been working night and day figuring out how to free Barry, although he's had to do it without the help of H.R. (Tom Cavanaugh). Julian Albert (Tom Felton) fell in love with Caitlin Snow (Danielle Panabaker), but her alter ego Killer Frost has no use for him. And what of Tracy Brand (Anne Dudek), the physicist they recruited to defeat Savitar? The budding romance she had with H.R. was cut short. Will Julian and Tracy still be around?

14 KNOW: WALLY WEST IS THE FLASH

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Of course, Team Flash can't leave Central City unprotected. Photos recently leaked out from The Flash set in Vancouver showing Kid Flash (Keiynan Lonsdale) in a partial Flash uniform, wearing distinctive red leggings. On Twitter, Candice Patton tried to throw fans off the trail with a tweet pointing out "kid flash has always had red pants ppl ... ." But other photos from the set show Lonsdale in full costume, and it's all red, and not Kid Flash's yellow and red.

However, Lonsdale, in an interview with Newsweek, indicated that the change is just temporary, "It's not something that's on my radar. I feel as though there is so much story to tell and Wally has so much growing to do. I'd like to see that journey continue."

13 KNOW: THE NEXT VILLAIN

The Thinker Neil Sandilands

After the Reverse-Flash in Season 1, Hunter Zolomon in Season 2 and Savitar in Season 3, we're all tired of The Flash facing off against speedsters. Producers agree, pledging that the next villain, The Thinker, will give Barry a run for his money in other ways -- like with his brilliant mind. The Flash panel at San Diego Comic-Con announced July 22 that Neil Sandilands from The 100s will be The Thinker, also known as Clifford DeVoe. During Season 3, DeVoe was mentioned by Abra Kadabra and by Savitar as a future Flash opponent.

In comics, DeVoe first appeared fighting original Flash Jay Garrick in All Flash #12 (September 1943), as a corrupt district attorney who partnered with a mobster he had prosecuted. DeVoe became a master plotter, and developed a "Thinking Cap" that emitted force beams. In modern times, The Thinker has been an artificial intelligence, doing its villainy via cyberspace. On TV, The Thinker got his start from the particle accelerator explosion.

12 KNOW: THE VILLAIN'S PARTNER

The Mechanic Kim Engelbrecht

A good villain is even better when he or she has the tools to torment our hero. For The Thinker, those gadgets are the handiwork of The Mechanic; after all, The Thinker is the ideas man, not one to get his hands dirty. The Thinker comes from the Golden Age of comics, but this version of The Thinker is new to TV. At San Diego Comic-Con, Kim Engelbrecht of Dominion was named as The Mechanic.

The casting note for the character describes her as "a highly intelligent engineer who designs and assembles a plethora of devices for the ailing Clifford DeVoe. DeVoe's right hand, she's the truest of true-believers who'll stop at nothing to implement his plan to fix all that's wrong with humanity -- even if she loses who she is in the process."

11 KNOW: THE ELONGATED MAN COMETH

Elongated Man

Another welcome addition to the show will be The Elongated Man. As a child, Ralph Dibny was fascinated with circus performers and took particular interest in finding out how contortionists do what they do. Noticing that all of them drink Gingold soda, the main ingredient of which is the gingo fruit from the Yucatan, Dibny synthesized a gingo concentrate. After he drank it, Dibny developed the ability to stretch and contort his body in amazing ways.

Not only is Dibny a scientist, he is also one of DC Comics' foremost detectives, first meeting The Scarlet Speedster in The Flash (Vol. 1) #112 (April-May 1960). That Silver Age origin could stand some updating for the TV screen, though it remains to be seen how. Perhaps the particle accelerator claimed another casualty? Casting notes call for a "Ryan Reynolds or Chris Pratt type," so take that for what it's worth!

10 KNOW: PEEK-A-BOO RETURNS

Peek-a-Boo

In Season 1, the villain Peek-a-Boo was a thorn in The Flash's side. She was Shawna Baez, another metahuman whose powers were awakened by the particle accelerator explosion. Played by Britne Oldford, Peek-a-Boo gained the ability to teleport, which she used to break her boyfriend out of prison and rob an armored truck on his behalf. Eventually, The Flash captured her. Later, Captain Cold and Golden Glider broke Peek-a-Boo and other villains out of the Pipeline in STAR Labs, and she hasn't been seen since.

Now she's back, slated to appear in the Season 4 premiere, although the reason why is not yet revealed. She'll likely be up against Wally, who hasn't met her before. Can he figure out how to handle her? And can Team Flash hold on to her this time?

9 KNOW: HARRISON WELLS IS BACK

The Flash HR Wells

One painful moment from "Finish Line" was the noble sacrifice of H.R. Wells, who disguised himself as Iris, took her place, and let Savitar stab him to death instead. The loss of H.R. leaves a hole in Team Flash aching to be filled ... by another version of Harrison Wells? Possibly. Tom Cavanagh has given us several turns of the character already, starting with the villainous version in Season 1 who was secretly the Reverse Flash.

Cavanagh is set to return next season, but which version of Wells will he be? The Wells of Earth-2 joined the team in Season 2, but went home; he returned to help defeat Savitar. But Cavanagh has several versions up his sleeve: "Twenty-seven! Twenty-seven subtle ones and four or five overt ones," he said in an interview at Comic Con International: San Diego in 2016.

8 RUMOR: WILL LOVE SET BARRY FREE?

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Wally and Jay Garrick (John Wesley Shipp) found their time in the Speed Force to be unending torment. But Barry was invited there by a vision of his mother Nora, who told him it would be a time of peace. The scene seemed to portend the "Terminal Velocity" storyline from The Flash (Vol. 2) #95-#100 (November 1994-April 1995), which established the Speed Force as part of DC Comics lore.

Wally was the title character in the comic then, and his love was Linda Park. Wally becomes one with the Speed Force, but still fights to protect Linda here on Earth. He breaks out, risking his own existence, because although being in the Speed Force seemed like heaven, she wasn't there with him. Wally's time in the Speed Force allowed him to master previously unknown ways to use his speed. But all the changes weren't positive.

7 RUMOR: DOES BARRY BECOME BLACK FLASH?

Black Flash chases Flash

The 2009 The Flash: Rebirth limited series (#1-#6, June 2009-April 2010) dealt with Barry Allen's return to the DC Universe after being killed in Crisis On Infinite Earths #8 (November 1985). Barry was first seen in DC Universe #0 (April 2008), and is fully freed from the Speed Force in Final Crisis #2 (August 2008). Rebirth brought him back to headline status in the DC Universe. One consequence of his emergence was being turned into the Black Flash -- a manifestation of death for DCU speedsters -- after the demise of the existing one.

The Black Flash appeared in TV's The Flash and in Legends of Tomorrow, and was destroyed by Killer Frost in "Finish Line." But nature, and the Speed Force, abhors a vacuum; it's possible that Barry could be turned into the Black Flash's replacement, just as in the comics.

6 RUMOR: THE NEXT ARROWVERSE CROSSOVER

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Plans are underway for the next teaming of the CW's superhero shows -- Supergirl, Arrow, Legends of Tomorrow and The Flash, although newcomer Black Lightning won't be part of the mix this go-round. No wonder the CW wants to do it again, as the crossover with Arrow and The Flash established Legends as a series. The "Invasion" matchup in 2016, which included Supergirl (though it had moved to the network after a season on CBS) gave the network its most-watched week since 2000, boosting viewership by 20% over the previous year.

In an Entertainment Weekly podcast, Arrow and Legends executive producer Marc Guggenheim pledged that the next crossover will do it better by doing it smaller; the goal is to "increase the emotional stakes and the emotional payoffs" along with delivering the action. But how can there be a crossover without Barry? We're not sure there will be -- maybe if he is Black Flash, he will actually be the villain!

5 RUMOR: A PEEK-A-BOO VS. KILLER FROST FIGHT?

Killer Frost The Flash

One of the mysteries of the new season is how Killer Frost fits into things. Caitlin Snow's ice powers awakened in Season 3 and, for reasons not explained, also slowly amped up her dark side. But in "Finish Line," Killer Frost had a last-minute change of heart and helped defeat Savitar by freezing him with her ice powers. She also refused to take the cure Julian offered, preferring to find her new path. The Flash Season 4 trailer shows Caitlin with her old look; did she change her mind? Or is Killer Frost still there, below the surface?

Another mystery is why Peek-a-Boo returns, although one motive might be revenge against Team Flash for keeping her in the Pipeline. So, what if she made a move on STAR Labs, and encountered Killer Frost? Frost is as likely to defend STAR Labs as she is to join Peek-a-Boo in the assault -- or fight her and then team up, in the time-honored superhero way.

4 RUMOR: MORE WEIRD (FUN) ONE-OFF EPISODES

Grant Gustin Melissa Benoist Duet

The title of the Season 4 premiere, "The Flash Reborn," could mean the show will ease up on the gloom clouding the recent run of episodes. One thing that made The Flash TV series stand out was that it had a lighter, happier tone than sister show Arrow. Over the second and especially third season, things became more grim and Barry became more angsty -- so much so that the song-and-dance crossover episode with Supergirl was a welcome change of pace.

Likewise, in "Cause and Effect," a bid to thwart Savitar by blocking Barry's ability to create memories backfires and Barry gets amnesia. But confused Barry is charming, lovable and funny! In fact, Iris is somewhat reluctant to change him back when it comes right down to it. The show needs the return of that kind of levity, and from what we hear, it may go back to that tried and true formula that made fans fall in love in the first place!

3 RUMOR: WILL BARRY MENTOR NEW SPEEDSTERS?

The Flash August Heart

On the other hand, "The Flash Reborn" could be a signal that the show will follow the 2016 "Rebirth" storyline from The Flash comics. In "Finish Line," the Speed Force storm was triggered by Jay Garrick's release from the prison within, which quieted only after Barry voluntarily took his place.

In The Flash (Vol. 5) #1-3 (August-September 2016), Central City is devastated by a Speed Force storm that washes over the citizens, turning several people into new speedsters who don't know how to use their powers. Barry trains them, although some turn to crime and one becomes the villain Godspeed. The TV Speed Force storm could have had the same result, creating new, amateur speedsters for Team Flash to handle -- which could be fun.

2 RUMOR: WILL CAPTAIN COLD CALL IN A FAVOR?

The Flash & Captain Cold

In Season 3's "Infantino Street," Iris' death at Savitar's hands was only 24 hours away. The Flash had a Speed Force bazooka that could trap Savitar, but needed massive power to operate it. Desperate, he opted to break into A.R.G.U.S. and steal its alien power crystal, taken from the Dominators in "Invasion." Knowing little about the fine arts of burglary, Barry brought in an expert: Captain Cold (Wentworth Miller).

Since Cold was inconveniently dead, Barry plucked him from the time stream while he was with the Legends of Tomorrow in 1892. What would Cold want in return for doing Barry this favor? Sure, Barry kept Cold from being eaten by Killer Shark on the way out of A.R.G.U.S., but that's not enough for Cold to call things even. It's always fun to see Cold do his thing, so let's hope the rumors are true and we see him again.

1 RUMOR: TEAM LEADER: CISCO OR IRIS?

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With Barry gone for an extended time, who takes the lead of Team Flash? Based on the trailer, it's a split decision! Best bud Cisco has the smarts and tech knowledge, and certainly will be committed to getting Barry out of the Speed Force. The Season 4 trailer shows Cisco using the Speed Force bazooka in one attempt, noting, "I made a few slight modifications, as Captain Solo would say." But Cisco may be distracted in his efforts, as romantic interest Gypsy (Jessica Camacho) is slated to appear in Season 4 on a recurring basis. And movie tough guy Danny Trejo will also be around as bounty hunter Breacher, Gypsy's overprotective father.

The Season 4 trailer shows Iris being steely in Barry's absence, telling her father Joe she won't "curl up in a ball and cry all day." However, Candice Patton told TV Line at the Saturn Awards that "Iris is really struggling to deal with that, and she does it in her own way." Hopefully, this means more moments where Iris takes initiative, like she did in "Finish Line" when she put two bullets into Savitar, or in "Welcome to Earth-2" where she was a detective with the Central City Police.

What are you looking forward to most in the new season of The Flash? Let us know in the comments!