The family way - Rhys Bowen

Molly Sullivan is a year into her marriage, expecting her first
child, and confined to the life of a housewife. She's restless and
irritable in the enforced idleness of pregnancy and the heat of a New
York summer in 1905. So when a trip to the post office brings a letter
addressed to her old detective agency asking her to locate a missing
Irish serving maid, Molly figures it couldn't hurt to at least ask
around, despite her promise to Daniel to give up her old career as a
detective. On the same day, Molly learns that five babies have been
kidnapped in the past month.
Refusing to let Molly help with the kidnapping investigation, Daniel
sends her away to spend the summer with his mother. But even in the
quiet, leafy suburbs, Molly's own pending motherhood makes her unable to
ignore these missing children. What she uncovers will lead her on a
terrifying journey through all levels of society, putting her life - and
that of her baby - in danger.