Lark! The Herald Angels Sing: A Meg Langslow Mystery by Donna Andrews
A note, attached to the baby girl's clothes, names the baby Lark and implicates Meg's brother, Rob, as the father. While a DNA test can reveal whether there's any truth to the accusation, Rob's afraid the mere suspicion could derail his plan to propose to the woman he loves. Meg soon discovers that the baby may be connected to something much bigger.