Complex sentence: Amen is also learning of the more secret parts of the family history, especially the death of an infant sister, and the mysterious Mr. Tominski, who might have saved her father's life as a child, but now inspires only fear in the children.
Split into simpler sentences: Amen is also learning of the more secret parts of the family's history, especially the death of an infant sister. The mysterious Mr. Tominski, who might have saved her father's life as a child, but now inspires only fear in the children.