The Secret Grave — Lois Ruby

Nightshade can be deadly.

Hannah and Scooter's sprawling, ramshackle house is named for the lethal plant that grows in the dark woods behind it. Hannah knows she's not supposed to explore the forest or nearby Moonlight Lake. But she's feeling lonely and desperate for an adventure. And there Hannah meets Cady, a mysterious girl who promises everything Hannah's been missing. Only Cady has a secret:

Cady wants Hannah all to herself.

Soon Cady is copying Hannah's style so they can be more alike. She lies to Hannah's friends, insults Scooter, and begs Hannah to break her parents' rules and sneak out for a midnight swim. Hannah wants to believe Cady's just a little insecure. But when she discovers a cemetery beyond the lake with an eerily familiar headstone, she must decide whether to trust her new friend or dig for answers that may lead her to a watery grave...