Breakups are always tough on the loved ones caught in the middle, and pets are no exception. Terriers brilliantly juxtaposes Britt and Katie's split against a flashback to the rape investigation that first brought Hank and Britt together.
Look, I don't mean to downplay the effects that dissolving relationships have on us humans, and neither does this series. In fact, Winston's presence in this scene serves to underscore the true feelings that Katie still harbors for the union that's just been shattered — feelings that the humans themselves are unable to communicate:
And just like that, it's over.
The rest of the episode deals with a pivotal case in the past of almost all of the Terriers regulars: a three-year-old serial rape investigation that Hank and Britt's new journalistic contact — the woman Hank saved in last week's episode — seems to have solved. Flashbacks tell most of the story, such as this scene where then-detective Hank and then-suspect Britt encounter each other for the first time in the OBPD interrogation room:
Hank comes away from that conversation convinced that Britt is innocent, but it takes a bit more to convince his colleagues:
The episode ends, however, on the opposite outcome of that clip above. Britt tracks down the classmate whom he thinks Katie seduced (not her actual paramour, the Naughty Professor) and beats him to a pulp. He's tossed in jail just as Hank and Detective Gustafson wrap the rape case, and the story comes full circle.
So... who was actually behind the sexual assaults? Looks like you're going to have to track down a full version of this episode to find out. I will say this: Detective Gustafson lays an ingenious trap for the perp using an otherwise-innocuous pair of womens' underpants.