The Summer of Broken Rules by K. L. Walther (paperback)

Paperback, in great condition, like new. When Meredith Fox lost her sister, Claire, eighteen months ago, she shut everyone out. But this summer she's determined to join the world again. The annual family vacation to Martha's Vineyard seems like the perfect place to reconnect. Her entire extended family is gathering for a big summer wedding, and although Meredith is dateless after being unexpectedly dumped, she's excited to participate in the traditional Fox family game of assassin that will take place during the week of wedding festivities. Claire always loved the game, and Meredith is determined to honor her legacy. But when Meredith forms an assassin alliance with a cute groomsman, she finds herself getting distracted. Meredith tries to focus on the game and win it for her sister, but she can't help falling for him. And as the week progresses, she realizes she's not only at risk of losing the game, but also her heart.