On Mac's flight to DC to testify, he winds up in a mile high crime scene when he finds an Air Marshal stabbed to death in the airplane bathroom and his gun is missing. Later, the team discovers the victim isn't an Air Marshal but rather a wanted felon who escaped custody and stole the Air Marshal's ID in an attempt to hijack the plane and flee the country. But with such a complicated plan the CSIs suspect the felon had to have an accomplice, making every passenger and crew member both witness and suspect.