Re the sentence: "At the core of Tom (Bird) and Lorna (Anderson's) story is the chilling question: How could evil lurk in the heart so close to piousness?"
For centuries, great evils have been concealed beneath fine dresses of piousness. Witness church-sponsored terror, Inquisitions, the Ayatollah, witch hunts, the Dark Ages and other horrors perpetrated in pious finery.
Piousness serve as such a great disguise because people expect, and want to expect, to find virtue pure as the driven snow beneath those skirts. A good rule of thumb may well be that the more piousness exhibited, the more evil likely to be found underneath.