I'm writing about two characters trying to solve a mystery. Right now I'm calling them Arthur and Helen. Helen works for a very secretive investigative unit. For instance they don't reveal to people that they are investigating a crime until after they've finished, and anyone who asks too many questions is given a number to call. They mysteriously stop asking questions by the next day. My problem is: I want Arthur to ask about a specific device that Helen has, and I want her to reply that she's not allowed to tell him about that. Then, several scenes later, I want that device to be what saves them from a tight spot. It's also meant to implicitly reveal some things about the agency she works for. Does this strike you as a deus ex machina? I'm planning it from the beginning so I hope that will remove that 'came out of nowhere' feeling that dei ex machina are known for. But at the same time, I'm not planning to drop any hints along the way about what it does (I don't see how I can without spoiling the whole thing). If you were reading this story, would such a thing surprise you or make you throw the book down in disgust?