After a government agency makes first contact with aliens in 1961, alien refugees live in secret on Earth by disguising themselves as humans in the New York metropolitan area. Men in Black (MIB) is a secret agency that polices these aliens, protects Earth from extraterrestrial threats and uses memory-erasing neuralyzers to keep alien activity a secret. MIB agents have their former identities erased while retired agents are neuralyzed and given new identities. After an operation to arrest an alien criminal named Mikey near the Mexican border by Agents K and D, the latter decides that he is too old for his job, prompting the former to neuralyze him so he can retire.
Meanwhile, NYPD officer James Darrell Edwards III pursues a unnaturally fast and agile suspect into the Solomon R. Guggenheim Museum. Impressed, K interviews James about his encounter, then neuralyzes him and leaves him a business card with an address. Edwards goes to the address and undergoes a series of tests, for which he finds unorthodox solutions, including a rational hesitation in a targeting test. While the other candidates, who are military-grade, are neuralyzed, K offers Edwards a position with the MIB. Edwards accepts and his identity and civilian life are erased as he becomes Agent J.