Linden and Holder, moments after figuring out that the Nicole/Ames meeting that led to Rosie’s murder was also attended by somebody from the Richmond campaign, are very nearly arrested before a last-minute “enemy of my enemy” deal puts them in cahoots with the Mayor’s people. Turns out those magic bones were part of some kind of escalating prank war that ultimately led to the faked photo from Season One, or something, but whatever: The campaign and its folks are the main target of the investigation once again.
How Linden and Holder do detective work throughout this episode is, they sit around in their car and make up wild theories and then act as if their wild theories are correct, and eventually — because the show is like this — they turn out to be correct. So they get Roberta to admit that Chief Nicole is an abusive lover and breaker-of-bones, and eventually twist her around into giving them this elevator footage that supposedly didn’t exist, which shows who the person is. (Also, it sounds like Roberta wasn’t the one that put up the haunted-tree picture, but whatever. I have a theory about that.*)
But first, there’s a lot of hilarious red-herring stuff where first you think it’s Jamie, then Gwen, then Jamie, then Gwen, then Holder and Linden split up and one of them thinks it’s Jamie, and the other one thinks it’s Gwen, but then they decide no, it’s Gwen and the other thinks it’s Jamie, and then they get back together and it’s like, “You got your Gwen theory in my Jamie theory! You got your Jamie theory in my Gwen theory!” Forever.