This in itself is pretty unbelievable. If someone I hadn't spoken to for five years suddenly asked me on holiday to Greece with them and their family, there would be red flags all over the place. But our MC just agrees to it.
And okay, I could have probably overlooked this but there were quite a lot of other not-quite-believable aspects to t he book too. The instalove (my pet peeve), the scary mean girl, the way everyone knows what the Big Secret is, except for our MC, the flakiness and apparent two-facedness of the ex-best-friend.
The romance was a bit of a turn-off. The MC starts off the book with a total bell-end of a boyfriend and doesn't get rid of him soon enough and then the next guy she falls for was a bit one-dimensional and he did really annoying things like ordering the MC's dinner for her (because the current year is apparently 1852).
This was an okay book for a quick read, but I wouldn't really recommend it.