Realizing Olivia can communicate with the possessed children, she and Wallace come up with a plan to rescue Marcus. Can they reach him before it's too late?

Lost in the maze-like tunnels leading to the Piper's lair, Olivia and Wallace continue their search for Marcus and the others. But they're not alone in the dark...the Piper's children are hunting them too. Can the sound of Olivia's voice lure out the good that is left?