A woman is killed during a party at a Star Island 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 young son, who Horatio wants to protect, refusing to let him testify.

E-mails and text messages trigger a mass gathering of students to perform a random task on a golf course. However, as the crowd disperses, the body of a high school student is found. The original message triggering the "flash mob" is traced to a high school senior whose father is a high-powered defense attorney. Meanwhile Horatio and Yelina investigate the death of a meth addict found in a dumpster outside where she buys the drugs.