WARSAW — Anna Misiewicz was just 7 years old when she was invited into the private chambers of her parish priest, in the small village of Topola in southwest Poland. She thought he wanted her to count church donations.

Instead, she found herself alone with a predator, identified only as Father Jan A. He touched her chest, stroked her body and forced her to use her hands to masturbate him.

Decades later, the smell of milk disgusts her still, she said, “because the priest would drink milk and the taste stayed on his mouth and lingered in mine.”

In a powerful new documentary that is rocking this deeply Roman Catholic nation, Ms. Misiewicz recalls these childhood nightmares, and then goes farther. She summons the courage to knock on the door of her abuser, a feeble old man but still a priest, and pose a simple question: Why?