This was an audiobook which failed for me. I didn't like the story and the reading by the curiously-named MacLeod Andrews was bad. The story started out just fine for the first chapter or so, but after that it devolved into tedious and stupid activities in which an irresponsible father trails four kids with him to Europe (and elsewhere, evidently) into dangerous situations, and then fails to go to the police, fails to get his kids out of danger, and in general just is a moron. These dimwits contaminate crime scenes and tamper with clues which could have led to a perceived suicide being seen by the police for the murder it was. I quickly decided this was too stupid to live. The fact that it's the start of a series is only one more reason to reject the mercenary heart of it.
It's a ridiculous Dan Brown-style story where some idiot leaves a trail marked by asinine cryptic clues for Becca, Darrel, Lily, and Wade, when all he had to do was make a phone call and tell his friend, or better yet, the police, what the deal was. Failing that, then at least post it on the Internet so the "shadowy" villains have no reason at all to chase your kids threateningly. It was profoundly dumb. I hope middle-graders are smart enough to see how silly this all is, and I feel sorry for those who are not, but of course, without this level of stupidity, there couldn't be a six book series, and neither the author nor the publisher would get rich off the allowances of middle-graders, would they now?