Too much suspension of disbelief. X is too American, too hysterical, and too much. Marc is hot, but too good to be true.
This book wound me up with all the mysteries and steamy sex... the hot Italian rich guy, the hint of mafia, and the strangeness of the Mysteries that X (Alexandra) agrees to take part in. She does so, because Marc (the hot Italian billionaire) has passed into the Fifth Mystery; the only way that she can continue to be with him is if she agrees to also achieve the Fifth Mystery.
BUT... for all of that, there's just a general weirdness. Naples and the surrounding area is described as trashy - literally, trash piled up in the streets, because of some mafia garbage thing. And dangerous. And X is such an American 21 year old. She irritates me with her decisions to pursue things and go into dangerous places just because SHE wants answers... or to explore... or something.
And her behavior at the Mysteries is abominable. OK, so it's probably scary. And no, I probably wouldn't like to be paraded around like that, either. BUT, everyone in this group has been through this; and no one seems to be leering or treating her badly. X gets hysterical too easily. But at the end, we're supposed to believe she's sucked it up enough to do what she did? Hmmmm....
Also too convenient that X is able to get answers from a big mafia guy and be able to get his cooperation not just once, but twice. She also "solves" the Mysteries. Ha!