A young woman, having witnessed an alien encounter as a child and escaping her memory neuralyzation, spends years searching for the secret organization she saw that day. Her intelligence and determination pay off when she finally tracks down the Men In Black (MIB), a covert agency that polices and monitors extraterrestrial interactions on Earth. Impressed by her skills and tenacity, the MIB recruits her as Agent M. As a probationary agent, she's assigned to the organization's London branch, where she's eager to prove her worth.

In London, Agent M partners with the branch's top agent, Agent H, a charismatic but somewhat unorthodox MIB operative. The pair are soon tasked with a seemingly routine mission: to liaise with an alien dignitary. However, their assignment quickly spirals into a global crisis when they uncover evidence of a mole within the MIB organization. This discovery leads them on a wild adventure filled with high-tech gadgets, shapeshifting aliens, and intergalactic intrigue as they race against time to identify the traitor and prevent a catastrophe that threatens the MIB and Earth's safety.