The film rests almost entirely on the shoulders of its two leads. Tilda Swinton is perfectly cast as the skeptical, intellectual Alithea. She brings a grounded humanity to the magical proceedings. Idris Elba, buried under intricate makeup and prosthetics, brings a tragic nobility to the Djinn. He is not a mischievous genie like in Disney cartoons; he is an ancient, lonely being suffering from a "longing" that has spanned millennia.