For Secrets, the fun doesn’t end once you’ve completed the story and collected the Silver Box. Afterward, you can aim for mastery of the Secret--an exciting challenge with even greater rewards. The scenes will become tougher, which makes the final reward so much sweeter. Who knows, you might even uncover an extra Secret once you’ve mastered every scene in the event!
Once you've completed the story and collected the Silver Box, the Mastery Challenge will start. You can see how close you are on the progress bar in the Secret Study.