The 6th Target by James Patterson, Maxine Paetro (2007, Hardcover)

When a horrifying attack leaves one of the four members
of the Women's Murder Club struggling for her life, the
others fight to keep a madman behind bars before anyone
else is hurt. And Lindsay Boxer and her new partner in the
San Francisco police department run flat-out to stop a series
of kidnappings that has electrified the city: children are
being plucked off the streets together with their nannies--
but the kidnappers aren't demanding ransom. Amid
uncertainty and rising panic, Lindsay juggles the possibility
of a new love with an unsolvable investigation, and the
knowledge that one member of the club could be on the
brink of death.
And just when everything appears momentarily under
control, the case takes a terrifying turn, putting an entire
city in lethal danger. Lindsay must make a choice she never
dreamed she'd face--with no certainty that either outcome
has more than a prayer of success.