There are two main plots, with Jesse Stone working on the murder of a mobster and Sunny Randall working to remove a young woman from a religious cult. Both plots are thin, and so they're padded out with many visits by Stone and Randall to their respective shrinks (Randall's is Susan Silverman, whose clothes and manner Randall admires as much as Spenser does). Meanwhile, the Stone/Randall personal relationship is developing.
The dialog's sharp, and I laughed, but even I have to admit that the book's just not very good. I hope the remaining Spenser novels are better.