When Det. Mac Taylor (Gary Sinise) and his team last tried chasing down a professional hitman ("Down the Rabbit Hole"), surprises came at every turn. For starters, the person they were looking for ended up being female. She was good, very good! Mac nearly caught her, but she escaped. Mac had to be reminded of serial killer Shane Casey since he sensed he was being closely watched ("Hung Out to Dry").
NYPD decides to inform the public about the situation on Crime Catchers, a show which lets people call in a tip anonymously. This works, and Mac, Det. Stella Bonasera (Melina Kanakaredes), Det. Don Flack (Eddie Cahill), and Det. Jessica Angell (Emanuelle Vaugier) take a trip out to an abandoned warehouse. They take the precaution of wearing Kevlar vests. After all, their suspect has killed a politician already.
They find their woman, dead. Mac confirms it's her. Processing the scene is simple enough, but the multiple computer screens give Mac an idea. Adam Ross (AJ Buckley), a CSI technician, soon arrives to go through hard drives.
When the team realizes the victim is someone else entirely, more questions remain. Det. Danny Messer (Carmine Giovinazzo), checks the Missing Persons file and discovers the victim is Katie Mann, a staff member working for the Mayor.
A sting is set up using SWAT, Angell, and the FBI. When the hitwoman is spooked, she takes off running. Mac races after her, letting everyone know where he's going. The last time he went after a suspect by himself, Caly Dobson jumped off a skyscraper roof ("Past Imperfect").
Before everyone else can step in, Mac has won a firefight with Suspect X (Kam Heskin, Passions). He gets her to tell him what it feels like to kill another, and she says she felt she was sending her victim to a better place.