Okay, so I have this idea for a major twist at the end of a book (to set up the next one) but it hinges on a conspiracy. Without giving too much away, here goes: At the end of the book, the book's secondary villain (secondary in the series, but the main one for the book in question) is about to be imprisoned. She breaks free, kills the guard and releases a fellow prisoner (the main villain of the series). The prisoner's escape was planned out by a politician who wants to use the prisoner, and the havoc he will invariably cause, to further his political career. So the bare bones of it is, the prisoner gets released and is allowed to cause havoc, in turn, he must help the politician with his goals. Does this sound like a plausible conspiracy or is it a little weak?
A story concept means nothing. I can tell you now, it has all been done before. What matters is how you write it, the characterization, the flow, the imagery, all of it. There's no benefit in asking what other people think of the concept! They'll either say,"Sounds great," or, "it sounds like a ripoff of..." If the idea stirs you, write it. Then ask people what they think of the final story. After they tell you what they don't like about it, revise it, usually several times, until you're happy with it or until you throw up your hands and say the hell with it. Please read What is Plot Creation and Development? Whether it is plausible is a matter of how well you sell it. How well you write it.
It sounds very plausible. Don't mind Cog. He's supposed to drive home valid points. Really, just try your idea out, and then come back and post the draft. Members here are pleased to review new material, especially when the concept is similar to yours.
Conspiracies aren't always plausible in the way people make them. Sometimes the implausibility might make them more viable of an option.
Basically when you look at popular conspiracy theories like the 9/11 thing that says it was an inside job, with all of the evidence anyone brings up the biggest defense is "but its highly implausible that they would do that". While I don't think that this is what really happened, I can see how someone can sit there and say "they did it because people would think that its implausible and that's why no one would think it was true." What makes a good conspiracy is when the elements are in the face of everyone, but the idea implausibility still exists because the motives are so well hidden and hard to guess that no one has really found them.
Truth is stranger than fiction... it's taken me a while to realise it really isn't what your write, but how If the characters don't act out of character (that's a bad way of saying they don't do anything the reader wouldn't accept, having followed your characters this far), coupled with the fact that your plot point does sound plausible, there is absolutely no reason why you shouldn't include it fiction's fun, anything can happen...
Conspiracies can never be too far out. Never. Spice it up with some ancient Egyptians, some crashed UFOs and the Illuminati! EDIT: Please note that this is my post number 747, which happens to be the type of plane used on the attack at World Trade Center. A councidence? Maybe. Maybe not.