Agent J (Will Smith) goes back in time to 1969 to prevent the death of his partner, Agent K (Tommy Lee Jones), by "Boris the Animal", a disgusting alien who has escaped from his prison on the moon and wants to lead an invasion on Earth. Back in time, Agent J must deal with a younger version of his partner (portrayed by Josh Brolin, who has the Tommy Lee Jones impression down pat). It seems that Agent K was interested in agent O (Alice Eve of The Raven) but never pursued it. In fact, the entire reason why he's so emotionless in his job is explained. Part 3 is as good as the first film, far better than the second, and links everything together.