Law & Order: CI Season 4 Episode 18 The Good Child

Goren and Eames are called in to investigate the murder of a young girl in a wealthy Manhattan family who is found strangled in her bed. The victim's parents, a well-respected doctor and an elegant socialite, are naturally shaken by the news and insist they have no idea who could have committed such a heinous crime.

As the detectives dig deeper, they discover that the victim's older sister, who has Down syndrome, may have witnessed the crime but is unable to communicate what she saw. The sister appears to have been ignored by the family, who has focused all their attention on the "perfect" younger sister.

As Goren and Eames continue to investigate, they discover that the victim was not as perfect as her family would like everyone to believe. She had several secrets, including a secret boyfriend and a troubled past, which may have contributed to her demise.

As the detectives close in on the killer, they realize that the victim's family will do anything to protect their own reputation and are willing to take drastic measures to keep their secrets from being exposed.

In the end, Goren and Eames are able to solve the case and bring justice for the young victim, but not without revealing some uncomfortable truths about the victim's family and the lengths they were willing to go to protect their image.