Rogue One is set a few months to a year before the events of the 1977 movie Episode IV: A New Hope (i.e. "the first one"). It features the first Death Star in the final stages of construction. The nascent Rebel Alliance has got wind that the Empire is testing a new weapon but has no idea beyond that what is going on. They enlist the reluctant aid of a band of mercenaries and rogues to send them on what appears to be a suicide mission to gain intelligence about the Imperial weapon...the same intelligence that later falls into the hands of Princess Leia and R2-D2, sparking the events of the entire saga.
Rogue One stars the Oscar and BAFTA-nominated Felicity Jones as Jyn Erso, an apparent mercenary and renegade against the Empire. She is "persuaded" to join the Rebel Alliance and take command of the mission to investigate the Empire's new weapon.
Erso is sent on her mission by Mon Mothma, the commander of the Rebel Alliance. Mothma previously appeared in Episode VI: Return of the Jedi, played by Caroline Blakiston, and in a deleted scene from Episode III: Revenge of the Sith, played by Genevieve O'Reilly. Not confirmed at the moment, it looks like O'Reilly is playing the role in Rogue One as well.
Diego Luna is playing an unspecified role, but he looks like a Rebel officer assigned to work with Erso.
This appears to be Alistair Petrie, who is playing a Rebel general.
Hollywood veteran Forrest Whitaker is playing another one of Erso's soldiers. It looks like he's the grizzled old veteran of the group.
Jiang Wen is playing another one of Erso's troops.
Donnie Yen, a Chinese martial artist and experienced actor, is playing another one of Erso's troops, apparently one who favours melee and unarmed combat over blasters. Yen's casting was counted a major coup by the production.
Ben Mendelsohn is playing an Imperial officer. From his rank insignia and uniform, it looks like he might be playing a Grand Admiral of the Imperial Starfleet, although sadly not fan-favourite novel character Thrawn. Some have speculated that Mendelsohn was playing Grand Moff Tarkin (played by the late Peter Cushing in the original Episode IV), but the different costume seems to rule that out.
The will be partly set in the Rebel base on Yavin IV, which appeared at the end of A New Hope. An old-school X-wing fighter can be seen in the background here.
The Death Star is in the final stages of construction at this time. Its superlaser focusing disc is being put into place here.
An Imperial-class Star Destroyer near the Death Star. In a nice nod to continuity, this appears to be an ImpStar One (Imperial I-class), highlighted by the diagonally-supported tractor beam array between the sensor globes. A significant number of ImpStar Ones were replaced or refitted as Imperial II-class Star Destroyers (or ImpStar Deuces) before the events of The Empire Strikes Back.
Imperial AT-ATs in a tropical setting.
Ben Mendelsohn's character surveys the aftermath of a battle. What appears to be the wreckage of a Rebel Y-wing can be seen in the background.
A hooded figure flanked by Imperial Guardsmen. This character is unknown, but does not appear to be Darth Vader (who is rumoured, but not confirmed, to have a cameo).
The title card for the movie.
The film is directed by Gareth Edwards, who helmed the well-received Monsters as well as the recent Godzilla reboot. According to Edwards, Rogue One will not feature any Jedi, lightsabres or the Force and will instead by a war story with "less clear-cut" heroes and villains than the other films. The Dirty Dozen has been cited as an inspiration. Producer Kathleen Kennedy has indicated that Rogue One, as not part of the core, Skywalker-focused saga, will allow different aesthetics, directorial and editing styles to be used compared to the main films.
Star Wars: Rogue One hits cinemas on 18 December.