The first trailer has already premiered for Assassin’s Creed, giving fans their first look at the big screen adaptation of the popular video game series. And all the staples of the gameplay were there: numerous rooftops, acrobatic fights, extreme parkour, and even a death defying leap of faith.

What the trailer also featured was a good primer on how Assassin’s Creed is set concurrently in the present and the past, introducing the Animus and its ability to allow descendants to live out the memories of their ancestors in real time. (Think of it like a virtual reality simulator where you can spend a day in the life of a long dead relative.)

The film isn’t a direct adaptation of any specific Assassin’s Creed game, but instead an original story starring Michael Fassbender in the roles of both Callum Lynch, a death row inmate, and his 15th century ancestor, the Spanish assassin, Aguilar. While on the set of Assassin’s Creed last year, Screen Rant had the opportunity to talk with Fassbender about his dual characters, specifically asking how, besides them existing in wildly different time periods, was he able to differentiate between the two characters:

As anyone who’s ever played an Assassin’s Creed game can attest, far more time is spent in the past, exploring the memories of your character’s ancestor, than in the present day. For the film, however, it appears there will be a stronger balance between the sequences in the past and the present. The trailer alone features quite a bit of Fassbender as the present day-Callum, incorporating the newly designed Animus (which appears to mimic his movements during the regressions) into scenes that will play in both the past and present.

“Well, one doesn’t say a lot and the other does. [laughs] Basically, in this story, we have somebody who doesn’t realize where he’s coming from. He doesn’t have a lineage that he can sort of feel a belonging to. So that’s one modern day sort of protagonist, Cal. He doesn’t realize he’s an assassin. He’s a bit of a sort of lost soul. He’s always sort of been drifting in and out of correctional facilities.

Then, of course, Aguilar is very much somebody that belongs to the creed. He has a cause. He’s sort of been following that cause. He belongs to it. So there are the two different very standpoints to the character. Hopefully Aguilar will teach Cal from the regressions that he does belong to. That’s essentially the main difference between the two characters.”

Of course, there are also plenty of shots in the Assassin’s Creed trailer that show Aguilar running across rooftops and performing stealthy assassinations – the sort of material fans would expect from an Assassin’s Creed movie – but it sure seems the film gives equal attention to his descendant. If that’s the case, then assuming Callum acquires that sense of belonging Fassbender mentions, future films could potentially continue his training through the memories of other ancestors, following the game’s pattern of featuring different time periods with each iteration.

Assassin’s Creed arrives in theaters on December 21, 2016. Keep an eye out for more details from our visit to the Assassin’s Creed set, coming soon!