Warning: possible spoiler
When Agent J (Will Smith) learns that Agent K's life, and the fate of earth, are in danger, he must travel back in time to prevent a catastrophic event. Ironically, he ends up teaming with a young Agent K (Josh Brolin) to stop it.
J also learns there are secrets that his partner had not told him.
The special effects are unbelievable, particularly that aliens often appear so quickly it appears like out of nowhere. Lots of action, and a better-than-expected story. Will Smith is charming and witty as usual, but Josh Brolin is especially good in his role.
Content warning: the first 15 minutes has two gross scenes. Tough it out, because it's worth it: at the end, the whole audience applauded.