A Heart of Gold is a fanfic by Muppet Central forum user Together Again/Silly Toga/Lisa. You can find it here. Keep in mind that it's on a forum so there are going to be posts in between chapters.
The story follows Kermit. He has been serving in the military for 10 months, but is honorably discharged when he is shot in the shoulder. Everyone is very happy that he's home, but Kermit has done something... Something that he refuses to forgive himself for...
The fanfic "A Heart of Gold" provides examples of:
- Abusive Parent: Betty Sue and Craig have a slightly abusive and alcoholic dad, though he's only really "abusive" when he's drunk. Otherwise than that, he's actually pretty nice.
- Adult Fear: The Child Corps. Also, in Chapter 68 when Robin goes missing. He's found though. And the oil rig getting destroyed by terrorists.
- Darker and Edgier: Compared to the quirky and hilarious show, this fic is pretty dark.
- Heroic B.S.O.D.: Kermit gets this after he kills a little boy.