Dilts and Grashaw build out “What Josiah Saw” thoughtfully, letting the dread from one story bleed into the next, until everything is covered in a dark, dark stain.

The family trauma is so clotted-thick, a faster pace and tightened-up editing might have eradicated the slow-motion underwater feel of the whole.

It has a stubborn, almost literary feel for character that accumulates a baleful momentum by the time the finale hits.

A deeply disturbing and novelistic tale of generational trauma and the horrors it holds.