The plot is choppy at first and jumps around making it disjointed at times. I had problems visualizing scenes and some chapter transitions could have been more interwoven with the two parallel storylines. The plot starts to pull together by the end, but it barely held my interest as it sets up the action for later in the story. Once the kids are on their own and get into the clues and solving the mystery, my interest returned. The cliff hanger ending was terrific and book one is a complete story in itself. I don't mind cliff hangers when it is after the resolution. When they chop the story off in the middle of the action it reads like a cliff hacker, not cliff hanger. This one is well done.
The characters don't have much internal changes and are somewhat forgettable which for me was the greatest weakness in the story. If the characters are not interesting then the book becomes a nebulous mass in my memory. The characters do have distinctive traits, they just lack a interesting arc: Becca is the shy, brilliant linguistic girl; Lily is the computer researching guru; Wade is the smart scientist and astrologist; and Darrel is the musician. They don't really fight among themselves and their interactions are mainly figuring out the mystery. I'm not sure Wade's story arc. I don't think he has one. He's interested in Becca and doesn't know how to deal with it, but there's not much to even that. He and Darrell are stepbrothers but they get along better than siblings. I wanted more dynamics between characters. Something. Anything. I didn't buy Becca being that language proficient, but then I've bumbled my way around so many different countries that most of those situations in books don't read authentic to me. I needed more regarding the villain. She's one dimensional and seems more of an enchantress than anything else. I wanted more background information and suppose it will probably occur in the sequel.
This is the first in a series and I'm sure the characters will get more fleshed out in continuing books. Other reviews have compared it to Dan Brown's "The Da Vinci Code." Brown's mystery is in pursuit of the Holy Grail and Mary Magdalene's role in the history of Christianity; whereas this story is the pursuit of 12 relics to construct a machine that Copernicus built. The kids speculate whether or not Copernicus messed around with history, but nothing is determined and will most likely be revealed in subsequent books. While I liked the premise, the book fell short of its potential by holding back too much plot information.