In the fifth episode of the six-part story arc "The Keys of Marinus," the Doctor (William Hartnell) and his companions have managed to locate three of the four keys needed to sustain the omnipotent Conscience of Marinus. It hasn't been easy, what with the terrors inherent in the city of Morphoton, the Screaming Jungle, and the snowy Marinus wilderness. But worse is still to come; upon arriving in the city of Millenius, the time travellers are arrested for murder and sentenced to immediate execution. Written by Terry Nation, "Sentence of Death" originally aired on May 9, 1964. ~ Hal Erickson, Rovi