The deaths by suicide of every adult in the Starnes scientific expedition on Triacus, driven to despair by the entity Gorgan, which then used their children to seize the Enterprise.
In the Original Series episode And the Children Shall Lead, the Enterprise answers a distress call from Triacus and finds the adults of Professor Starnes's expedition dead by their own hands. Their five children, led by Tommy Starnes, play happily among the bodies and show no grief at all.
Once aboard, the children summon their friendly angel, Gorgan, a survivor of a band of marauders once based on the planet. He has given them the power to control adults through their deepest fears and means to reach the colony on Marcos XII and build a following there. The bridge crew are soon paralysed by illusions, and two security men are beamed into empty space.
Kirk breaks the hold by playing the expedition's own recordings, showing the children their parents alive and then their graves. As they weep, Gorgan's fair face decays and he fades away.