On Writing After Reading "On Writing."

What to do when your plot explodes?

It's all Stephen King's fault.  At least, he started it.  A week or so ago, I was doing a quick read of his memoir/craft guide On Writing to decide whether I was going to finish it or send it back to the library.  I landed on his section on not plotting.  You should here that I am a serious plotted, outliner, and all-around planner of everything, novel included.

Mr. King writes "A strong situation renders the whole question of the plot moot, which is fine with me.  The most interesting situations can usually be expressed as a What-if question."  Hmm, I thought.  What is my "What If"?

It went something like this - "What if, um, your mom dies and you don't know who your father is, so you're sent to live with your evil headmistress who wants to steal your inheritance and then you find out your father's name but it's really common so you have to travel all over the country to figure out who he is?"  

In other words, what if plotty plot plot to plot plot, plot-plot-plot, PLOT happened?  Which doesn't even get to the whole magic part of the story, which is one of my favorite parts and ought to somehow be central!  Could this be, I thought, why I can never answer the question "What're you writing about?" in one, cohesive sentence?

Yes, of course that's it.  Because since then my plot has exploded.  Almost immediately after reading this, my brain fevered-out and I started questioning everything I though I'd written in stone - characters who were dead are now all alive, in one form or another, pseudo-science is now magic, romantic pairing now cousins - the list goes on.  I couldn't believe how many plot turnarounds my subconscious had been storing up to pour forth in this one moment of frenzied, panicked notebook scribbling.

So what exactly do you do when you're a full outline and 5 chapters into a draft with a synopsis and first chapter due for manuscript critique in a few weeks and now your story wants to change?  

Get to work, I suppose.  le sigh.

Has this happened to you?  I'm going to be fine, right?