Mac is called in when an abandoned briefcase discovered on the trading floor of a mercantile exchange yields not a bomb but blood evidence from the owner, who has gone missing. The investigation quickly centers on a man involved in illegal trading.

A private plane crashes in a swamp, killing seven of the eight passengers onboard, and Caine immediately suspects foul play. Complicating things for Caine is the return, after six months, of Senior CSI Megan Donner (Kim Delaney), whose job he now has.