The second book introduces a few more characters so the casting for the film is ongoing. Today it has been announced that Kim Basinger will join the cast, in the very important role of Elana Lincoln. She had a former relationship with Christian Grey (that's Jamie Dornan) and a very complicated one as she was the dominant and there are suggestions that it bordered on abusive. As with everything else in the books, it's all far from subtle.
Basinger is a big name to attract to the piece, though at 62 she's a good 20 years older than described in the book. Her character is set to go toe to toe with Dakota Johnson's Anastasia so the scene is set for some tense moments. Otherwise there's a little more to the second story, with a stalker character and the increased pressure to try to create a 'normal' relationship along lines that Grey can understand.
Fifty Shades Darker is in cinemas in February 2017, Fifty Shades Freed will follow a year later.