Right after reading The Summoning, I had to get my hands on the sequel, since it ended in a MASSSIVE cliffhanger.
The Awakening is about Chloe, a necromancer who is now on the run with three other kids from a group of people who want to do experiments on them. I'd say more, but then I'd give too much away.
The Awakening completely makes up for the fact that The Summoning was more of an introduction book. There's so much action and many cliff hangers on every chapter, but I never got bored and I always wanted more. I enjoyed the characters' interactions and the writing was as fantastic as ever. There are STILL so many questions that need to be answered! I can't wait for The Reckoning in 2010!