Shortly before Horatio is set to testify at a high-profile murder case in which the defendant is the husband of a city councilwoman, he's given new facts that could prove the man is innocent. The information revolves around the discovery of a second victim who matches the profile of the first one and was killed in a similar manner. If the man on trial isn't guilty, then Horatio fears that a serial killer may be on the loose.

An explosion in a rundown barn nearly kills Horatio and his crew just after they find a dead man inside, bound with duct tape. The case gets personal for Horatio when he discovers that the leading suspect knew his late brother. Meanwhile, Alexx is shocked to learn that her best friend's husband has been murdered, apparently the victim of a random shooting.

A woman is killed during a posh party at an exclusive waterfront estate when a man opens fire on the proceedings from a cigarette boat. When a former con is arrested, he acts as his own lawyer and proves to be smarter than he appears. Complicating matters is the fact that the leading witness in the case is the dead woman's 10-year-old son, whom Horatio wants to protect, refusing to let him testify.

Horatio's life is changed forever when he learns important information about his deceased brother. Horatio must now figure out what to do with this information about his brother, Raymond, and whether or not to tell Yelina. Meanwhile, the team investigates when a woman is murdered at a crowded bar after she's approached by a female employee of a service that helps men pick-up women. Also, when Delko loses his badge after some reckless behavior and it's used in a crime, he must locate the badge before it's used again.

An axe murderer on death row is given a stay of execution just moments before it was to take place, on the grounds that there may have been tainted DNA analysis used at his trial. Now, without using any DNA evidence, the team must race against time and reexamine all of the physical evidence in the case, just as they get a call on a new double murder that looks suspiciously like the case they're working on.