Sydney Walsh

When the chief investigator of a controversial report documenting corruption within the NYPD is gunned down the day before his findings are published, Mac and Stella must find the killer, launching a massive search that makes every officer listed in the report a suspect. Meanwhile, Danny and Aiden investigate the murder of a gypsy cab driver.

A family feud threatens a girl's chance for getting a bone-marrow transplant; Greene admits his father, who has pneumonia.

Joe begins to fear for his daughter's life when Allison cannot get a murderer, who kills young women, out of her head.

A case, involving a missing prostitute who recently attempted suicide, serves to teach a rookie investigator that she has a lot to learn about the Missing Person's Squad.

When Julia surprises Matt having sex with both Vanessa Bartholomew (recurring guest star Kate Mara) and Ridley Lange (recurring guest star Sophia Bush), she humiliates him by demanding an intervention with Ridley's nonplussed mother and Vanessa's outraged parents, who didn't even know that Vanessa is a lesbian.

The couple shares common ground with new friends Bob and Carol Stanford (Antonio Sabato Jr., Sydney Walsh); Bob has a secret, evil identity.