Horatio suspects that a disgraced graduate psychology student is killing the people who caused her to fail, and is leaving cryptic messages for the crime lab. However, could it actually be part of an even more sinister plan?
A man falls to his death from a skyscraper window, and the new M.E. is shot and killed at the scene. The crimes are soon connected to ammunition dealers, an ATF agent, and Horatio's son Kyle's new stepfather.
Calleigh is in a coma after a smoke inhalation injury sustained while investigating a case involving a dead doctor, drug dealers, and black market organ transplants.
The body of the witness Julia Winston paid off in Horatio's son's trial is found in a swamp, but Horatio's investigation is interrupted by his extradition to Brazil to face murder charges. Meanwhile, Calleigh is kidnapped.
The state's attorney Delko has been working with is killed by a car bomb. The car was stolen from Evidence just like the diamonds from the earlier case, and the evidence soon leads back to Wolfe.
Calleigh's kidnappers use her to try and cover up a shooting death that they committed. However, she discovers that the gunshot is not what killed the victim. Meanwhile, CSI uncovers more clues in the death of the trial witness.
A young woman dies from carbon monoxide poisoning but the man with her survives, in what appears to be a suicide pact related to their credit card debt. Meanwhile, Delko starts seeing his dead colleague, Tim Speedle.