The little girl and her sister were taken from a flood ravaged New Orleans by a child predator. While looking for the sister, the perpetrator while in their custody gets very sick and dies. He's been exposed to the anthrax virus. When Benson and Stabler find the sister, she too has been exposed.
On top of this story from the beginning is Jackson Settle from the fictional New York Ledger. The man ultimately responsible for the theft of the anthrax vials from a New Orleans based laboratory is one creepy Leo Marks.
It's Settle and Mariska Hargitay's relationship with him that's the centerpiece of this episode. As long as journalists like him can pursue the truth we will be a free country.
What happens with him and Olivia is the reason to watch this episode.