Murder in the Hamptons by Amy Garvey

From the back cover:

Maggie Harding has a few rules for living. Order, control, and carefully checked-off to do-lists equal a safe life. Safe is good. What’s not good is, oh, hmmm, maybe having a wild, passionate, naked pizza-eating weekend fling with type A  Brody, the kind of guy who leaves a girl shaken and stirred, deep down. Bad. Bad, bad, bad. What to do? Run away. Constraint is better than chaos. Right?

So what’s that same girl to do when she runs into the guy five years later at a big Hamptons bash, and he’s staring at her with that naughty, right-here-right-now grin, while she’s trying not to make an idiot of herself in front of lots of rich people and “It” list Hollywood stars? Make another run for it. Except that she can’t. Because somebody’s dead on the lawn and “house party” has just become “house arrest”. The only way out of this insanity is for Maggie to find the murderer herself, even if the biggest mystery is why she ever belived that saying good-bye to Tyler was the right thing to do…

ISBN 0-7582-1041-8