Lal, a member of a technologically-advanced race known as the Vians, subjected Captain James T. Kirk, Spock and Dr. McCoy to a "study" that used thought alone to test the survival thresholds of those participating in the study. By inflicting injuries upon the landing party-turned-test subjects, Lal's study ultimately determined whether or not Gem, a functioning empath, and her race were worth saving from their doomed sun. Lal's methods allowed him to observe and judge Gem's empathic reponses in terms of compassion and self-sacrifice. Gem's abilities allowed her to heal the test subjects, particularly Kirk, as easily as Lal inflicted them.
Lal was one of two Vians present during the study. On stardate 5121.5, Lal's study was a "success," and he concluded that Gem's species was worthy of survival.