Boris the Animal (Jemaine Clement) intends to go back in time and eliminate the person who captured him – Agent K – after escaping from LunarMax, a moon-based maximum security jail (Josh Brolin). When he does so, Agent J (Will Smith) discovers that the timeline has been altered and returns to July 15, 1969, the day before Agent K is killed. After overcoming some skepticism, J persuades young K and others of who he is and why he is there. They track Boris down with the help of Griffin (Michael Stuhlbarg), a being who can see all timelines. J also discovers a truth that old Agent K (Tommy Lee Jones) had never revealed to him.