The Swan House by Elizabeth Musser

From Goodreads:

Mary Swan Middleton has always taken for granted the advantages of her family's wealth. But a tragedy that touches all of Atlanta sends her reeling in grief. When the family maid challenges her to reach out to the less fortunate as a way to ease her own pain, Mary Swan meets Carl-and everything changes. For although Carl is her opposite in nearly every way, he has something her privileged life could not give her. And when she seeks his help to uncover a mystery, she learns far more than she ever could have imagined.