It is the summer of 1925. Emily Stewart and her brother, Michael, are thirteen-year-old twins—privileged, precocious, and wandering aimlessly around their family's Philadelphia estate. One day Emily discovers an odd physical talent—she can secretly crack a joint in her ankle so the sound seems to burst in midair from nowhere. In their garden tea house, Emily and Michael gather the neighborhood children to fool them with these "spirit knockings." But soon this game of contacting the dead creeps into a world of adults still reeling from a world war. And when the twins find themselves dabbling in the uncertain territory of human grief and family secrets, their game spins out of control...