Drew already posted the trailer, but my direct comment became so long that I think it might work better as an additional article. I apologize! Okay, pure speculation ahead – I think this is what happens plotwise, deduced from the trailer and from scenes that were filmed outside:
(includes descriptions of several scenes that weren’t in the trailer, but had been spotted during outdoor shoots)
Regarding 2:22 – as Batman won’t be much of a presence in this, I believe we’ll only see the Caped Crusader in a short prologue. We’ll see how both the Joker and Harley get caught by Batman (who uses the Batmobile to do so), and how they are getting brought to Belle Reve and sent to maximum security.
Trailer opening – Waller sits down with two government officials and tells them about her black ops project Suicide Squad. She gets the funding for it, and assembles said team that consists of Harley, Boomerang, Diablo, Deadshot, Slipknot, Katana, and Rick Flag (not Enchantress!). They all probably get poisoned in order to forget about escaping, and Flag is most certainly Waller’s watch dog to keep eyes on them.
As for the most important scene beginning at 2:38 – the Joker saying that he’s “not going to kill someone, just hurt s.o. really, really bad”. You might have spotted the torn and smeared Robin costume in the Batman V Superman trailer, and you might speculate that we’ll get to see how the Joker tortures and kills Batman’s boy wonder. I don’t think so. Check out mark 1:35. That is the exact same room in which the Joker shows up at the end of the trailer. Shivering bald guy by the way seems to be Hugo Strange. In an earlier scene, a bearded man in a blue suit, probably Joker’s man Jonny Frost, throws a blond doctor onto a gurney in that room. I believe that woman is Dr Harleen Quinzel, and that the Joker speaks those threatening lines to her. I think this is a flashback in which we get to see her getting brainwashed into Harley Quinn.
There’s just one scene of hers I can’t really bring into place. Ayer filmed an outdoor scene in which Harleen (normal looking) follows the Joker’s car on a motorcycle and stops him. The Joker gets out and begins to talk to her while she aims a gun at him. A trucker appears, offers her his help, but Harleen suddenly shoots that guy. The Joker then takes her gun away and bitchslaps her so hard that she falls down. If it’s a later scene, I can’t understand why she would look normal and aim a gun at him. But if it’s a scene from the prologue, why bother visiting her a second time with a bunch of goons?
Back to the trailer at 1:56 – the Deadshot flashback shows that he’s caring for a little girl, therefore he’s probably to be seen as a good guy. Seeing that girl again will be Deadshot’s biggest motivation. I don’t think we’ll see flashbacks for the supporting goons Slipknot, Killer Croc, and El Diablo.
However, 0:34 and 1:40 show the origin of Enchantress. Exploring a cave, she (as a normal woman) seems to find something that gives her magical abilities. Also note that she seems to be the girlfriend of Rick Flag (1:58). I’ll get back to that.
There were multiple rumors that Jesse Eisenberg would be involved as Lex Luthor in some capacity, and I kinda bet that the main objective of the Suicide Squad mission is to break into one of his technology headquarters. After all, Batman V Superman introduces kryptonite, and if the rumors are true, we’ll also be seeing Luthor’s fighting suit AND Doomsday as well, probably another creation of Luthor. The government would have more than enough reasons for wanting that technology, and who would be more believable as thieves stupid enough to rob from Luthor than a bunch of crazy villains? Luthor has probably top notch defense systems, and it’ll be outright suicide to go against that. Hence the name.
But they probably won’t be able to just begin their heist. They’ll need to distract the police first, therefore they’ll go to downtown and create a little chaos. It’ll be Flag’s job to keep the numbers of collateral damage low, and they’ll probably pay visits to several smaller villains such as King Shark or the tattooed guy Common plays. Maybe Harley goes undercover as a stripper at King Shark’s club (1:59)?
2:25 – shows someone breaking into Belle Reve, maybe El Diablo? I’m sure that the Joker outsmarts everyone and has one or more guys on the team secretly preparing his escape.
I could believe that, in the end, Harley gets caught once more and that she gets freed by Mr J, Note that in her introducing scene in prison, Harley’s hair is completely blond (1:02). At 2:26, it seems that she’s back in prison, but her hair has the coloring.
At 2:14 – the Joker and his goons with Batman and panda masks infiltrate some sort of factory. Doesn’t really look like something Lex Luthor would build, but maybe it’s just a hideout? It’ll most certainly be one of the final scenes of the movie as the Joker is now free again.
It can be guaranteed that Waller eventually screws the team over and sends those attack helicopters (2:02) to wipe them all out. Whatever they gonna find that Waller is really after, it’ll probably be something dangerous, especially for people with abilities. And having a girlfriend with new-found magical powers will probably lead to SWAT’s Flag changing sides. Flag has been rumored to be a villain for quite some time, but it’s possible that both Flag and Deadshot end up being the good guys of them all. Just note how at 1:57 Deadshot hugs his daughter, and next scene is Flag kissing his girlfriend.
One last thing. The element of water seems to be of some importance. The trailer opens with rain, it rains during Enchantress’s cave visit, she even sits in water, 2:25 has El Diablo doing something with fire admist tons of water, 2:25 has a soaked Harley, seemingly in prison, 2:28 has El Diablo getting flushed away, and you’ve probably seen the leaked set image of Deadshot carrying a completely soaked Harley through the rain.