Missy altered the atmospheric temperance field in the Sunken Desert to alter the brainwaves of all visitors, making them believe they were in the middle of a battlefield. This changed the molecular structure of the sound waves, making those affected far more aggressive. She also "conveniently" left a small arsenal, providing weapons for the sudden onset of war. In fact, they had all come to have picnics and were complete strangers.
Around two days in, the Lumiat used a paradigm nebuliser to reverse what Missy had done. The visitors were horrified by their actions, once they remembered the truth. (AUDIO: The Lumiat)