What's it all about?: The power and confusion of Sicario

Sicario is a movie that you have to take on two levels: One one plane it's a story about a group of rogue CIA officers, military combat vets, FBI agents, and a recruited drug-cartel expert from South America who uncover a scene of grisly execution and set off to nail the head of the Mexican drug cartel that called the shots. On this level, the movie is gripping from start to finish, with some terrifically tense scenes, notably the discover of the mass killings at the outset, a scary journey into the heart of Juarez in search of a kingpin, the invasion of the smugglers tunnel leading into the Mexican desert, the final approach to the drug lord - well-paced, terrific pounding music, and at least once cool tough-guy character (played by Josh Brolin) who holds out interest. That said, there's a second plane: the plot itself is so elaborate, confusing, and in fact on looking back kind of ridiculous that it's almost impossible to figure out what's going on; and the two central characters, a man and woman (Emily Blunt) FBI agents as so bland that I kept wondering what they hell are they doing on this mission, or in this movie? There's a really thin attempt to explain why these novices are on the ride: the CIA guys say they need an FBI member of their troupe in order to justify acting outside of U.S. borders. Really? Or did I miss something? And if you need an FBI agent to come along why not a veteran rather than a doe-eyed novice who will gawk in surprise and awe at everything she sees - other than to give Brolin a reason to explain things to her and thereby to us? So overall it's one of those powerful movies that has you in its grip for two hours and when it's done you have to wonder whether any of it made sense and what mission was all about.