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Peter Jackson’s latest literary adaptation keeps moving at a steady pace, as Variety reports that his Mortal Engines movie has just cast one of its lead actors. Robbie Sheehan’s (Fortitude) role isn’t currently known, but he will lead the cast. The dystopian steampunk world of The Mortal Engines source book—which is driven by “Municipal Darwinism,” in which larger cities consume smaller ones for their resources—should allow him to strap on interesting gadgets or at least some goggles. But Sheehan is probably already hoping this YA adaptation will fare better than The Mortal Instruments: City Of Bones, which he starred in back in 2013.

Also joining the cast is Fantastic Beasts And Where To Find Them’s Ronan Raftery, who has a supporting, also undisclosed, role. Jackson’s reassembled his usual team for the movie; he’ll produce and co-write with Fran Walsh and Philippa Boyens, while his protege Christian Rivers will make his directorial debut. Mortal Engines pulls into theaters December 14, 2018.