What Time Is It There? - The Bean Books, #3

Just over a year ago, Bean and Zak headed for colleges two thousand miles apart, promising to write, but to see other people . until Bean fell for the wrong guy and Zak fell off the planet. Now, Bean's got two weeks' worth of Zak's year-old letters that she still can't bear to open-and a broken heart. Her new best friend, a guy named Amp, wants her to read the letters and be done with it, but he may have his own reasons for that.
When Sam shows up at Bean's school unexpectedly and Bean tumbles into the 19th century from the cellar of a ruined church, things start making a bizarre kind of sense. That is, if she can just fit all the pieces together again.