When Boris the Animal (Jemaine Clement), an alien who is the last of his race, is confined to LunarMax, a penal colony on the moon, he escapes and goes to Earth to get the man who placed him there, M.I.B. Agent K (Tommy Lee Jones). He confronts K, K and J (Will Smith) corner him, but he disappears. J asks K who he is, but K doesn't want to say anything. J goes to M.I.B. Headquarters and learns who Boris is, but before he could learn more, the Agent in charge, O (Dame Emma Thompson), stops him. The next day, J goes to pick up K, but finds someone else living at his apartment. When he goes to M.I.B., he looks for K, but everyone there tells him, K died in 1969 after tackling with Boris. But J says K captured him. That's when alien vessels which are from Boris' planet show up, and they're about to devour the Earth. But J says that K placed a barrier that keeps them from entering Earth in 1969, which would lead to their extinction. It's obvious that Boris went back in time and killed K before he could deploy the barrier. So J goes to see an alien on Earth whose father was also at the penal colony, who J assumes told Boris that he worked on time travel and his son has the device. J goes to see him and tells him about the invasion. So he sends J back just before K's death. J arrives in 1969 and fails to stop Boris and is captured by the younger K (Josh Brolin) who asks him who he is, and what is he doing here. J was told not to tell him anything. But with time running out J tells him, but K doesn't believe him at first, so they go out to stop Boris. Only problem, J doesn't exactly know what happened, so he's not sure where they should go.