The Summer of Broken Rules by K.L. Walther

Meredith Fox has been going to Martha's Vineyard for the summer as long as she can remember. But this summer is the first one back since the death of Meredith's sister. It will all be overwhelming, but even more since since the entire extended family will be together for her cousin's big wedding.

Unfortunately, Meredith's longtime boyfriend unexpectedly dumped her two weeks before the wedding, leaving her dateless. Luckily, she has the perfect distraction. Her family has a tradition of playing the ultimate game of Assassin every summer, and this year it will take place during the week of wedding festivities.