Fuzzy navel - Joe Konrath

Life's pretty good for Lieutenant Daniels. She's solved some of the city's toughest and most high profile homicides. Her fiance, Latham, is on the mend from an almost deadly case of botulism. She's just learnt that Alex Kork, one of the sickest, most dangerous criminals Jack ever put away, has killed herself. But things quickly take a turn for the worse when a group of vigilantes on a murderous spree takes down a cop. Then things turn downright ugly when Jack learns that Alex may not have killed herself after all...