Simplify the following text for a Grade 4 native English-speaking person.
Original: The release of the Flood prompts 343 Guilty Spark to recruit the Master Chief in retrieving the Index , a device that will activate Halo and prevent the Flood from spreading beyond the facility .
Simplified: It is named 343 Guilty Spark . It explains that he should turn on Halo 's weapons to destroy the Flood .