Bloodstream by Tess Gerritsen
In April came the rains. In August came the heat. In November came the horror. It's paying a return visit. Lapped by the gentle waters of Locust Lake, the small resort town of Tranquility, Maine, seems like the perfect spot for Dr Claire Elliot to shelter her adolescent son, Noah, from the temptations of the big city and the lingering memory of his father's death. And she's hopeful that she can earn the trust of the town as she builds a new practice. But all her plans unravel with the onset of winter when a rash of teenage violence, far more deadly than anything she'd encountered in the city, erupts in the local school. As she tries to find a medical explanation for this murderous epidemic, Claire stumbles upon an insidious evil which has blighted the town's past and threatens its future. Fearful that Noah, too, is at risk, she must race to prove her theory before everything she loves is destroyed.