This is an excellent post by Livia Blackburne (via the PV comments--read 'em!) about writing a book description. I especially like this part:

To make up an example [of a straightforward story summary]: "Stacy loses her favorite puppy, but thankfully tracks it down after several days. Then she realizes that a dog-napping ring was behind it all. She works out an arrangement with the neighborhood dogwalkers, and together they disrupt the ring."

When writing a pitch, it can be tempting to summarize both the conflicts and the resolutions equally. But instead, try emphasizing the problems more than the resolutions.

"Stacy loses her favorite puppy, and her investigations lead her to a horrible dognapping ring. Now, her only hope is to work with the annoying and unfriendly neighborhood dogwalkers, and if she doesn’t succeed, all the dogs in her city will die."

Remember, the point of any description or summary is to make the person think, "I want to read that book!" They're not going to think that if you tell them that everything works out in the end.