The novel has a life of its own!

Interestingly, my novel draft is taking on its own life!  The characters are telling me how they want to proceed, and I may agree.  There are two directions as I approach the third part...and I am undecided.  Who is in charge? Darned if I know.  Maybe many writers find this happening.  You plan it out, then find yourself in a segue - not necessarily good - but it may take you somewhere more thrilling or of interest to the reader.  Hmmm...now I must decide which way a reader would prefer, then NOT do that?  Do I want to surprise the reader, shock them, or satisfy?