Complex sentence: But when he reveals the shocking truth--she's only half human, a clone from a hybrid (Sil and Eve) of human and alien DNA--they must flee to Mexico to locate the scientist who created her.
Split into simpler sentences: But when he reveals the shocking truth... she's only half human, a clone from a hybrid (Sil and Eve) of human and alien DNA. They must flee to Mexico to locate the scientist who created her.