Annika Peterson

Routine disposal of drug evidence goes horribly wrong, leaving two police officers dead and the CSI team under investigation.

Joan discovers an unsolved murder connected to a rare prehistoric fossil when she reviews one of Sherlock's cold cases; Sherlock's responsibilities as a sobriety sponsor cross personal boundaries.

Charlie convinces Don to launch an investigation when an engineering student is found dead from an apparent suicide.

After a neighbor is killed, Allison installs a high-tech burglar alarm that she thinks may be communicating with Marie.

Mac believes he can fight the internal affairs investigation that is about to be started against him because of what happened to Clay Dobson. Can Mac explain what happened to the suspect he was chasing and will it be good enough for him to keep his job? Also Stella could lose her job as a CSI after a cold case is somehow connected to her.