Clone trooper Tup succumbs to a mysterious mental illness that results in the shocking death of a Jedi Master. Unable to account for his murderous actions, Tup is sedated and sent back to Kamino for examination. Anakin and ARC trooper Fives accompany Tup, but their return trip is ambushed by Separatists.

Clone trooper Tup is scheduled for transport to Coruscant, where the Supreme Chancellor's own doctors will closely examine him. Fives breaks protocol and defies orders to dig up answers, and discovers that there is an organic construct of unknown purpose hidden in the brains of all clone troopers.