Fans of Vince Flynn's Mitch Rapp novels were thrilled to learn earlier this year that a film adaptation of American Assassin was officially underway. The series of novels, which began in 1999 and so far runs 15 books long, follows Mitch Rapp as he fights terrorist attacks against the United States as an undercover CIA operative. American Assassin, chronologically the first book in the series but the eleventh to be published, provides an origin story of sorts for Rapp.

The American Assassin film adaptation has been in the planning stage since 2012, with Chris Hemsworth and Bruce Willis originally courted for the leading roles. Earlier this fall, we released images and a full synopsis that revealed that, instead, Maze Runner star Dylan O'Brien and former Batman Michael Keaton had nabbed the parts of Mitch Rapp and Stan Hurley, respectively. Many fans were surprised to learn that O'Brien had been cast to play the part, as some have interpreted Rapp's in-book description as in shape to mean he is extremely muscular. Others thought O'Brien perfectly captured the "everyman" aspect of Rapp, as well as his lacrosse-player's build. No matter where you stand on the American Assassin casting, we've just received more images that can help you decide whether this adaptation will be a hit or a flop.

A series of photos debuted by USA Today and feaured on Collider show the diverse cast in action and in character as filming begins in London. Check out our gallery, below, for first looks at Taylor Kitsch as the movie's villain, Michael Keaton as Stan Hurley, and Sanaa Lathan as Irene Kennedy.

[vn_gallery name="American Assassin Movie Images" id="834439"]

Whether or not these images match the ones in your head for the lively American Assassin universe, it's great to see the novel brought to life. We get glimpses of Rapp in all different stages of his training (we almost didn't recognize O'Brien behind that enormous beard), as well as mentors Hurley and Kennedy. If these images are any indication, this is shaping up to be an action-packed origin story, the likes of which we've been unable to see in other secret agent franchises like Jason Bourne.

Though these images don't necessarily tell us much about the film itself in terms of script or execution, we do get to see the characters behind Amerucan Assassin brought to life. We hope that this complex world transfers nearly enough to film, and that our high hopes for O'Brien and Keaton aren't dashed -- though we're going to wait until we get the full movie, or at least a trailer, before we roll out the judgment.

American Assassin doesn't have an official release date yet. We'll let you know when that changes.

Source: Collider, USA Today