A meeting in a London bus with jewel thief Lady Christina takes a turn for the worst for the Doctor when the bus takes a detour to a desert-like planet, where the deadly Swarm awaits.
Based on actual events of American serial killer Edmund Kemper, who murdered his grandparents at age 15 and, after being paroled for that crime, killed eight women in 1972 and 1973 including his own mother.