When Alexis's little sister Kasey becomes obsessed with an antique doll, Alexis thinks she is just being her usual weird self. Things get weirder, though, when their house starts changing. Doors open and close by themselves; water boils on the unlit stove; and an unplugged air conditioner blasts cold air. Kasey is changing, too. Her blue eyes go green, she starts using old-fashioned language, and she forgets chunks of time. Most disturbing of all is the dangerous new chip on Kasey's shoulder. The formerly gentle child is gone, and the new Kasey is . Alexis is the only one who can stop her sister -- but what if that green-eyed girl isn't even Kasey anymore?