Actually a bit beyond the midpoint, but Bulgakov makes it a focus of change:
We have no idea whether there were any other strange occurrences in Moscow that night, and we have no intention of trying to find out, since the time has come for us to proceed to Part Two of this true narrative. Follow me, reader! (p. 181)
The last several pages indeed been strange, as Bulgakov intrudes upon his story to directly address the reader. All the magic that had happened at the magic show that evening reversed itself; women who had gladly ran onstage and grabbed new fancy dresses in exchange for their own, found themselves wandering around in their underwear once outside the theater. The ten-ruble notes that fell from the ceiling turned into useless bits of paper which you can imagine caused all sorts of problems when used for purchases, or they turned into foreign currency which got the holders into serious trouble with the government.
There is a color, a vibrancy about the odd trio of Woland, Korovyov and the black cat that is in direct contrast with the drabness of Moscow life at the time. It is no wonder that the devil is so readily accepted into their world, and the devil himself knows the time is ripe. People are repressed and desperate, most warily cautious and resigned, those who rebell, go missing.
We’ve seen just a bit of the Master and Margarita, and I presume that the story may refocus on them as we follow Bulgakov deeper into his world.