To me, it seems like Professor Randolph or Mr. Parrish are the ones up to no good-Mr. Hurst does have some motives but he doesn't strike as the scheming kind(unless it's a scheme to get more wine in his glass!).

Mr. Parrish seems devoted but appearances are decieving as we all know,plus asking Lizzie for a lock of her hair was odd;why didn't Parrish think to ask Mr. Darcy as well for one of his?

Professor Randolph also has the appearance of goodness but he seemed most eager to support Parrish's idea of taking Caroline out of the country so,hmm....