The Cape area (Martha's Vineyard) also figures in Linda Fairstein's "The Kills." Part of the Alexandra Cooper (a Manhattan sex crimes prosecutor just like the author) series, the plot was too complicated for me, involving coin collecting, rich people, and not-so-rich people. For a New Yorker, Alex drove an awful lot (perhaps as a DA, she didn't feel safe on public transportation).
Also taking place in Boston area (just trying to find a unifying thread here) is "The Sleeping Beauty Proposal" by Sarah Strohmeyer. Genie is an admissions counselor at a Tufts-like university, and has a professor/boyfriend who won't commit - until he writes a best-selling novel and proposes on national television. But not to her! He refuses to discuss it and leaves for his native England, while she lets her family think she's engaged and they make wedding plans. Oy! This had a light touch, but seemed unbelievable. Oh what a tangled web...
Another elaborate subterfuge underlies the British chick-lit book "Asking for Trouble" by Elizabeth Young. Sophy made up a boyfriend Dominic to keep her parents from nagging, but OOPS, she'll need to produce him for her sister's wedding. So she hires Josh and hilarity ensues. Pleasant enough, but it never really rings true. The basis for the movie "The Wedding Date" which I don't even remember reading about.
More engaging was "Confessions of a Shopaholic" by Sophie Kinsella. I really enjoyed the first book in this now-classic British chick-lit series. Becky cannot seem to stay out of debt, despite dire consequences, but somehow it's all charming and funny.