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. Racial tensions turned the prison into a pressure cooker that finally boiled over in an all-too-lethal fashion, leaving two inmates dead. One of the killings is an open-and-shut case, complete with eyewitnesses; but the other, the murder of a former cop, defies easy answers. Initial investigation of the crime scene points to one cause of death, but the CSI team's scientific methods uncover something completely different -- and wholly unexpected....

On the other edge of the city, Stella Bonasera and Lindsay Monroe look into the murder of a young woman who worked at a popular Italian bakery in the Bronx. They find the perfect suspect almost immediately: a frequent customer who spent a lot of time flirting with the victim and who previously had been arrested for a violent crime. Yet Stella can't help but think that their perfect suspect is just a little too perfect for such a messy murder....

Nothing is as it seems as New York City's dedicated crime scene investigators piece together the clues and examine the evidence to discover the true killers in their midst.