First off I should say I thoroughly enjoyed this film, even though I'm a bit of a Nolan detractor. The music score was particularly brilliant!
The plot was very easy to understand and I don't even think I need post a Spoiler Alert to continue here.
The plot was simply the discovering of the key to Inversion and Entropic Reverse-Inversion through the backwards/forward pseudo application of a Bio-metric Post Inversion Syndrome Counter-Therapy causing the fusion ratio to counterbalance Reverse Inversion in an artificial yet wholly concrete temporal visual time and space continuum. If you can grasp that, then the plot's a piece of cake.
You see when a coaxial reverse spectrum replicates itself within the manifest guidelines of an Inversion Sub-Environment, past and future temporal constructs diffuse, then reverse, then re-reverse into a predetermined yet fractured reorganization sequence which ultimately cancels then re-installs itself in order for the characters (and the audience) to establish who the heck they were all working for and what the heck they were all doing. Got it?