I have a special fondness for the theme of evil masquerading as good. I love villains who trick you into thinking they're good guys and then shock you when the time comes for them to show their true colors. In fact I submit that such villains would enjoy greater success than those who visibly flaunted their evilness, as they could more successfully manipulate genuinely good people into carrying out their agenda. I have an ostensibly sweet and cheerful young woman who tells the male hero that her people are under attack by a tyrannical sorceress and asks him to recover an object which is the source of the sorceress's power. The hero steals this object and gives it to the first woman only to discover that she's the real aggressor who wants to use the object for evil ends. From that point forward the hero joins the second woman's cause and must undo the damage he inflicted in the first act. My question is precisely how shocking my twist should be. Should I drop in a few clues that the second woman isn't the actual bad guy in the first act even before the big revelation? If so, while the hero might initially gloss over these clues due to his preconceptions, readers might figure the whole thing out prematurely.