These two had the best chemistry on and off the screen but one of my favorite films of their's is Adam's Rib (1949)--in which Hepburn and Tracy are a happily married couple Amanda and Adam Bonner. Adam is given a crime of passion type murder case as a prosecutor, and she chose to represent the defendant to prove a point about the disparity of treatment in the justice system between men and women. He believes all murder is wrong-and that no person has the right to take a life. no matter what the reasons are--it is unjustified. Pinky vs. Pinkie in the courtroom ensues (as they like to lovingly call one another) and it starts to affect their personal relationship in a major way.
Of course when a marriage is struggling to see eye to eye on a major issue such as the morality of murder against the importance of women's rights, it doesn't help that Kip, the smooth composer bachelor type neighbor has shown Amanda a bit of interest, he even wrote her a song entitled after her--and Adam is jealous and hurt that she took the case.
Their back and forth intertwining the case and their marriage and the hint of cuckolding--infidelity is seen as this taboo tantamount to murder. Its not put in those terms but the tongue in cheek and blatant displays of Adam being cuckolded and emasculated--his resistance on the basis that as a White Male, makes him such a great cuckold, he gets all cute and pissy. I am glad he is too moral to murder anyone but this film does highlight adultery in a way that appealed to me even as a kid growing up.