After Ivy Hon submits her DNA to a testing company, she’s delighted to learn that Lottie Montagne, a first cousin she never knew she had, is also on their registry, and she’s even more excited when Lottie invites her for a visit so that she can meet her other relatives—though not her mother, Tatum Caine, who vanished shortly after giving birth to Ivy and giving her up for adoption. But the fly in the ointment is a monster: Special Agent Ballo of the FBI tells Ivy that her DNA is also a match for the Full Moon Killer, who’s murdered at least eight young women since 1988 and who, after several years off, has recently come roaring back to life. As if it weren’t stressful enough to be introducing herself for the first time to her birth relatives—imperious Grandma Aggie; Aggie’s ex-cop son, Terry; her sister, Tristen the taxidermist; her disapproving brother, Phillip; and the blessedly normal-seeming Lottie—now Ivy has to wonder which one of them is a serial killer. It’s a great setup, but Marr, who zigzags among the viewpoints of Ivy, Tatum, and a third party who seems more and more likely to be the Full Moon Killer, keeps upping the stakes like a compulsive gambler. The childhood secrets! The seductive men! The abusive sex cult! The authority figures who can’t be trusted! And on top of everything else, the approach of the full moon!