Pathologist Maura Isles - an adopted child who never knew the identity of her birth parents - is confronted by the corpse of a murdered woman who is apparently her identical twin She launches an investigation, together with Detective Jane Rizzoli, into her sister's past, following the trail to a state correctional facility and a schizophrenic inmate who may be her mother This leads to a remote cabin in Maine, a killer who has been murdering expectant mothers for decades, making periodic sweeps of the country, and the kidnapping of an affluent pregnant housewife who is kept buried in a crude coffin