As Castle and Alexis travel to London, their routine flight turns deadly when the plane’s Air Marshal is found murdered. With the help of Beckett on the ground, Castle and Alexis race against time to find the killer before he carries out his fateful plan.
Castle and Alexis' tactic of using the victim's fingerprint to unlock his phone was also used in the Major Crimes episode Turn Down. In that case, the ME had to shock the corpse with a defibrillator for the idea to work as it was stated phones needed to read both the fingerprint and the electric charge running through a person's body to unlock a phone.
