In 2266, Lethe was committed to the colony, for rehabilitative therapy. After being rehabilitated, she stayed at the colony as a therapist. Dr. Tristan Adams judged her to be a very good therapist. She had a blank look which the other staff members and inmates of the colony also had; they had been victims of a neural neutralizer that Dr. Adams was experimentally using there.
Questioned about her offense by Captain Kirk, Lethe replied, "Does it matter? That person no longer exists." She described her previous self as a "different person – malignant, hateful." Dr. Helen Noel remarked that the shifting of memory patterns was basic to psychotherapy; Dr. Adams added that patients should not be required to relive the evils committed earlier in their lives, when they were ill. Lethe showed her loyalty to Dr. Adams by calling security on Dr. Noel. (TOS: "Dagger of the Mind")