The Gundam Wing movie takes place after the series ends.  A girl named Marimeia launches an attack on the Earth Sphere Unified Nations.  The Gundam Pilots and their allies (and enemies too) must battle overwhelming odds to save the world again.  The Endless Waltz has begun.

Review: Believe it or not, I found this much easier to understand than the series.  They laid the plot out before you and showed you what each character did to solve the problem.  I also liked the fact that characters who were originally enemies are now fighting along side each other.  Some of the characters appearances seems really contrived, especially Zechs, but it was well-done, like an orchestra (fitting for the title).  Get the DVD because it contains two versions, the TV version, and the OVA version.