Just ordered...

The new Karin Slaughter book UNDONE. I can't wait to read ...er...listen to it. (Ordered book on CD so I can listen on my way to work) Her last book was great so I have high expectations.
In the last book she killed off a very important character...at least, I think the character is dead...I won't know till I get my hands on UDONE.
My question is this...You have a good series going with two main characters. Well actually one would be the supremo main but the first secondary character is sooo important that when Karin axed him I almost dropped the book. I had to go back two pages and reread everything. I was in shock, yes there it was in black and white on the page...dead semi-main, killed, kaput, gonzo.
I immediately ran to her website to send her a "I can't believe you did that!" email. But she beat me to it. There on her web was a place that explained why she did it. Smart writer.
But really, do you owe your readers anything? Or is this what makes a great writer? The ability to surprise and shock?
And keep us coming back.