The following contains MAJOR spoilers for Mission: Impossible -- Fallout, so STOP READING if you haven't yet seen the newest Mission movie. And really, take the time to go see it!
In the latest Mission: Impossible, Ethan Hunt (Tom Cruise) is hot on the trail of a new threat known as the Apostles, led by the mysterious shadow agent identified only as John Lark. What Ethan doesn't realize, until it's almost too late, is that Lark is hiding in plain sight on Hunt's own IMF team... as we, the audience eventually figure out that Henry Cavill is John Lark, posing as CIA operative August Walker. This double cross requires that we go back and watch Mission: Impossible -- Fallout a second time, because once you realize Walker is dirty, you want to know how he manipulated Hunt without his own knowledge.
It also required that Henry Cavill stay light on his feet, as he told CinemaBlend that his character's methods and motivations changed frequently on set, as the screenplay shifted and shaped to meet new needs. Explaining the process of playing a double agent, Cavill confided to CinemaBlend:
It has been documented that Mission: Impossible -- Fallout went through script revisions over the course of its production, with Simon Pegg saying on record that they basically started filming without a complete script, and Christopher McQuarrie saying to CinemaBlend that the break in production forced by Tom Cruise's ankle injury allowed them the time to go over plot holes and properly fill them in. A lot of those changes rested on Henry Cavill's broad shoulders, as his character -- August Walker -- had the most to hide from Ethan Hunt, and he had to protect real secrets until the director chose to reveal them to the audience.
When we mentioned to Henry Cavill that rewriting his character on the fly must have been maddening for him, as an actor, he says that his complete trust in McQ allowed him to dive in with no reservations and find the performance that worked for the movie. Cavill admitted:
Based on audience reaction to Mission: Impossible -- Fallout, it certainly DID turn out fine. The movie is critically acclaimed, with a staggering 98% Fresh on Rotten Tomatoes. And it set a new high bar for box office, enjoying the biggest opening in franchise history. Here's Henry Cavill, explaining the joy (and challenges) with playing a double agent in the Mission: Impossible films: