The biggest conundrum of this book may be what on earth happens in the ending. Actually, let's rephrase that: why doesn't anything happen in the ending?
If you read this book and were waiting for the moment when Kathy, Tommy, Ruth, and the rest of the clones staged an uprising and join the Clone Liberation Army, then we're with you. Free the clones! Or even if they weren't going to revolt against the system, couldn't Kathy and her friends have just driven away? There don't seem to be any actual gates stopping them (check out the "Freedom and Confinement" theme for more on this subject), so what's wrong with a one-way ticket to Mexico?
But in the end, Kathy and her friends do nothing of the sort. In fact, they do nothing at all. Instead, they submit to their depressing fate (and both they and we know that this fate isn't a pretty one): donating organs and completing. They don't even consider fighting the system or running away. Kathy says it best with the final line of the book: "I just waited a bit, then turned back to the car, to drive off to wherever it was I was supposed to be" (23.49).
So why doesn't Kathy fight back? Why doesn't she drive away and declare herself free? (Head over to the "Passivity" theme and see if you can figure out why the characters are so submissive.) What is your reaction to Kathy's submission?