I really enjoyed this, but subtracted one star because I wished more had been explicitly concluded. This is a great combination of mystery, science inquiry, family and friend relationships, and history. Halfway through, I guessed something (view spoiler)[about Mallory's family (hide spoiler)] that I think most kids would puzzle out as well, but we never get our suspicions confirmed (or is it that obvious? or not true after all?). I especially liked how the kids evolved and learned to think for themselves, and to consider the truths of what their parents had told them. 
 I don't think the cover portrays how much of this is set in the modern day. I would have put a black and white photo of an old glass bottle of water on the cover, lit up from the side.