Four Walls

Detectives Mac Taylor, Danny Messer, Sheldon Hawkes and Don Flack are called in to investigate a double-homicide at a medium security facility on Staten Island. The prison has been witness to a lot of racially-motivated tensions and it appears that things have finally boiled over in a lethal fashion. One of the murders seems to be an open-and-shut case -- a prisoner gets a shiv in his ribs and everyone sees it happen -- but the other is more of a puzzle. At first glance it appears that the victim was killed with a blunt instrument to the head while he was working out in the weights room -- but the CSI team's lab work uncovers something very different...

Meanwhile, Detectives Stella Bonasera, Lindsay Monroe and Jennifer Angell look into the murder of a young woman who worked at a popular Italian bakery in the Bronx. There's a likely suspect, one who's been seen flirting with the victim and has a rap sheet for attempted rape -- but Stella isn't sure that everything is what it seems…