Erica Spindler: Shocking Pink [2006] paperback

I spy...murder...The mysterious lovers the three girls spied on were engaged in a deadly sexual game. No one else was supposed to know - especially not Andie and her friends. But curiosity can become obsession. Now, years later, someone is watching Andie. Someone who won't let her forget the unsolved murder of 'Mrs X'. Andie. Julie. Raven. Three very different women bound by much more than friendship. And they're about to discover that loyalty can be murder...