The Summer Guests by Tess Gerritsen

 This is the 2nd installment of the "Martini Club" series set in Maine. Maggie Bird and her merry band of retired CIA agents have settled in Maine and like to use their particular expertise to "help" interim police chief Jo Thibodeau. Their efforts jump into high gear when summer visitor Zoe Conover disappears. Her disappearance turns out to be related to some old bones found at the bottom of Maiden Pond but everyone struggles to figure out the connection. With interesting characters and a compelling plot, it's a perfect summer read.