This book is mightily ambitious and covers a lot of territory. Much of it is interesting, however I thought it moved pretty slowly for a middle-grade novel. The archeology aspect is undeniably fascinating, but there are lots of characters who are presented in a way which struck me as confusing. I had some trouble following who was whom and who was where and when. The brother-sister interaction was okay, though I thought they seemed more of an age than they were supposed to be. Evan seemed very young. The whole drug theme, with a student doing hands on research on the San Pedro hallucinogenic cactus experience, was kind of bizarre in a book for middle grade readers. Several plot holes are still nagging at me, and I didn't like the device of showing illustrations of ragged bits from Samantha's notebook about what was coming in the next chapter. I did really like the way Spanish vocabulary and phrases were incorporated throughout. I think I would have liked the book much better (for MG readers) if it was tighter, shorter and snappier. It would also have worked pretty well at this length as a YA with slightly older protagonists. I got this book free at ALA Midwinter.