Henry Muller packs the apartment of his recently deceased mother on the Lower East Side. A lonely man, he watches Grace Purefoy through the window, a young girl from the neighborhood on her way uptown to sell drugs for dealer, Justin. Later that night, Grace tells Justin she's done selling drugs. Justin objects and Grace runs for it. As if on cue, Henry opens his door and Grace slips inside. A familiar face from younger days, Grace trusts Henry. She takes a hot shower and by way of thanks, kisses Henry. The simple kiss unleashes years of repressed desire in Henry, and when Grace names Henry for what he is - a pervert – he kills her in a rage. Detectives Nichols and Eames must track down a killer who is surprisingly adept, and too close for comfort.
Sanitation workers discover Grace's body in a dumpster. When the prep school ID of Ceci Madison is found in a wallet and assumed to be hers, detectives Nichols and Wheeler are brought onto the case. A visit to Ceci's home tells Ceci is alive and well. Ceci bought marijuana from Grace the evening before, but couldn't make the full payment. Grace took Ceci's wallet for collateral.
M.E. Rodgers explains that Grace's killer bleached her inside and out. He didn't leave behind any forensic evidence; he knew what he was doing. By putting the body in a dumpster, there are cross-contamination issues. It was the perfect murder – untraceable.
The cops catch a break when they run Grace's fingerprints. A juvie record for possession gets them her name and last known address on the Lower East Side. Ross wants to kick the case to the local precinct: it's not a major case. Nichols appeals for a few more days, citing the sophistication of the killer as a possible interest to the Major Case Squad.
Wheeler, who is nine months pregnant, learns the baby is due imminently. Detective Eames is pulled onto the case.
Nichols and Eames pay a visit to Grace's sad home. Her mother, Karen, is an alcoholic. She explains that Grace used to hang out with someone named Paj. They learn that Grace had dreams of a healthier life, and planned on leaving the city. As the detectives leave, they meet Karen's equally sad drinking buddy, Nate.
Nichols, moved by Grace's clear desire for a better life, decides to take the little evidence that they have to the best forensic scientist in the city. We go to the forensic crime lab and meet... Henry Muller – the killer. He takes the case.
The detectives track down PAJ, which is an alias for Park Avenue Justin, aka Justin Lennox. He's a drug dealer for the kids uptown and he refuses to talk to the cops.
Meanwhile, Henry has learned that the lead suspect in Grace's case is Justin Lennox. He goes to the police evidence room and pulls out an old assault case against Justin Loomis. He finds a bloody shirt and cuts away a barely discernible sampling of a bloodstain.
Henry calls Nichols to his lab and hands him a report. He tells that he found a viable tissue sample beneath Grace's nails, and got a match in the system: Justin Loomis.
Confused by Henry's findings, Nichols approaches M.E. Rodgers for an explanation. She insists she went over the body herself, and has done so again recently, and there are no viable tissue samples. When he learns that Henry's mother lived across the street from Grace he approaches Ross with his suspicions about Henry. Ross dismisses the theory and tells him to check out Nate.
Nichols orchestrates an elaborate set up during a visit to Henry at the lab. While they talk, Henry sees a woman nearby wearing Grace's clothing and looking just like Grace. Nichols knows in that moment that Henry killed Grace, and Henry knows that Nichols knows.
Eames gets a report on some of Grace's clothing taken from her home: they have male semen on them. The detectives arrest Nate and bring him in for questioning.
Meanwhile, Rodgers approaches Henry for a favor. She explains that Nichols ordered expensive MRI imaging tests on Grace, which turned up a single hair from inside her body. It's likely the killer's. She hopes he will take a look at the hair. He will.
The detectives interrogate Nate, but are getting nowhere. Henry stops by to get a reference sample hair from the suspect, Nate. He takes a piece of Nate's hair to compare to the one given to him by Rodgers.
Henry types up his report and returns to the squad room with the news: the hairs are a DNA match. Nate is Grace's killer, he tells them.
In the final scene of the episode, Nichols tells Henry that the hair given to him by Rodgers was his own hair (Nichols'). Nichols puts the squeeze on Henry and the brilliant forensic scientist is shown to be a tortured, sexually repressed pedophile.