The Twin Dilemma

The Doctor has regenerated, having sacrificed his fifth persona to save Peri's life. But things are not going well. On this occasion the process of regeneration is by no means smooth, for the even-tempered, good-humored fifth Doctor has given way to a rather disturbed and unsettled successor. In a particularly irascible moment the new Doctor comes dangerously close to committing a shocking crime. Overwhelmed with guilt for his violent behavior, the repentant Time Lord decides to become a hermit.