Two sisters have always stood together. Now, they're the only ones left.

In the shadow of Mount Hood in the US Pacific Northwest, sixteen-year-old Tennant is checking rabbit traps with her eight-year-old sister Sophie.

The girls are suddenly overcome by a strange vibration rising out of the forest, building in intensity until it sounds like a deafening crescendo of screams.

From out of nowhere, their father sweeps them up and drops them through a trapdoor into a storm cellar. But the noise only gets worse . . .