61. In "Madam X" when Clark gives his "problem dropped on me" excuse Lois thinks it odd. The next part we do not see per se, but Lois will of couse pay attention to all Superman sightings, and so she will read about Superman rescuing the falling worker that morning. She then puts two and two togerther and realizes that CK=SM.
I like this one because it involes Lois using more investigative skill than some.
