This was originally planned to be based on The Seven Crystal Balls and Prisoners of the Sun, however screenwriter Anthony Horowitz has since called this into question, suggesting these films would be the second sequel and another story would become the first sequel.12 In February 2012, Spielberg revealed to Total Film that they had completed a story outline for the sequel. He also said that the film will be based on more than one book, but no more than two.6 In May 2012, Anthony Horowitz said that in Tintin II we "can expect to meet Cuthbert Calculus."7