God yeah chris! I have experienced this--and it hurts like hell, doesn't it?! So frustrating, my sympathy goes out to you. I hope you don't have to go right back to the drawingboard???
b*******! How dare they? I think you should buy some crayons and draw all over their precious bloody book. Then put some nice colourful pictures on your thesis. Flowers maybe. Or a little kitten. and a smily face. That can be the originality bit.
I have often imagined sending a thesis to my supervisors with puppies and kittens in it, a few flowers, and happy faces - and my preface would read (verbatim):
" I wrote bout animals cos I fink they r well cute"
The book arrived. I read it - it is magisterial. My thesis is ravaged, I will have change chunks - but thank god, she has ommited to look at something I was signficantly looking at. So relief and tears in (unequal) measure.
maybe you could use your own research and state that a lot of your views are similar to that of an independent other ressource (this book) and this confirms the strength of your argument.
Look on the bright side - at least it means you're on the right track, and not writing daft nonesense :) If a good academic is replicating your ideas, then they must be good! Chin up.