It’s all change for the adaptation of Vince Flynn potboiler American Assassin, as Jeffrey Nachmanoff has signed on to take over writing and directing duties from Ed Zwick.

The Love And Other Drugs co-writer/director has dropped out because he’s going to be too busy directing Legendary East’s The Great Wall and CBS Films has decided that it didn’t want to wait for him to be available.

Now Nachmanoff will tackle directing the book which, although it’s Flynn’s 11th in the series, flashes back to follow the origin story of the central hero, Mitch Rapp.

It turns out that Rapp had been a high-flying college student and promising athlete until a tragedy saw him switch career paths and become one of the most dedicated terrorist hunters working with the CIA. No decision has been made on who'll play Rapp: while actors like Matthew Fox, Gerard Butler and Colin Farrell had been possibilities when the film was a straight adventure, the producers are now looking for someone a little younger.

Nachmanoff has some experience with spies and double crosses, having co-written and directed Traitor. He’s also been working behind the camera for ace US conspiracy series Homeland. And his script for Last Stand will soon be on screen, starring Arnold Schwarzenegger as the small town sheriff who has to deal with a crime lord making a bolt for the Mexican border through his territory.