Is it possible for a movie to be brainy and stupid at the same time? Luc Besson's "Lucy," in which Scarlett Johansson plays a superwoman able to play god with her scientifically enhanced mind, makes a pretty compelling case. Besson, who hasn't directed a satisfying action vehicle since "The Fifth Element" in 1997, doesn't exactly return to form here so much as scatter it all over the place, with the committed Johansson providing a unifying force at the center of the madness. Though Besson's screenplay toys clumsily with big ideas involving the history of human consciousness, the plot is simple: The Tapei-based Lucy (Johansson) agrees to deliver a package to the mob on behalf of her boyfriend, who's promptly killed.