The Silent Spy
At first, when Nancy tries to call Savannah, he hangs up on her, but Bess and George distract him so that she can talk to her. Later, when Nancy wants a copy of Savannah's book, Bess goes on a date with Logan to get it. He tells Nancy that he started working for Savannah a few years back as a fill-in gig during spring break, but the job was just too weird to quit. By Ghost of Thornton Hall, though, he was "fired" and she is moving on.
In The Silent Spy, when Nancy is reading the Cathedral archives, she discovers that informant "L. M." has said that in Kyoto, Nancy is disturbing "family S." and is driven to "solve the case" of the mother's death, and that the psychology present here is clear.