The Rat King

The episode was viewed by 3.69 million people, earning a 0.8/3 in the 18-49 rating demographics on the Nielson ratings scale, ranking second on its timeslot and ninth for the night in the 18-49 demographics, behind a rerun of Blue Bloods, Dateline NBC, MasterChef Junior, The Amazing Race, 20/20, Dr. Ken, Last Man Standing, and Shark Tank.[1] This was a 2% increase in viewership from the previous episode, which was watched by 3.62 million viewers with a 0.9/3.[2] This means that 0.8 percent of all households with televisions watched the episode, while 3 percent of all households watching television at that time watched it. With DVR factoring in, the episode was watched by 6.11 million viewers and had a 1.6 ratings share in the 18-49 demographics.[3]

"The Rat King" received generally positive reviews. Les Chappell from The A.V. Club gave the episode a "B" rating and wrote, "'The Rat King' is one of those episodes of Grimm that decides to forego its byzantine plotting and elaborate wesen social structuring in favor of doing something truly crazy, and the explanation this week — that Reinigen can bond together in a process involving cancer-like cells — is out there even for this show. Unfortunately, it does so in an episode that's also trying to do the aforementioned plotting and social structuring, and the marriage between the two prevents either part from connecting."[4]

Kathleen Wiedel from TV Fanatic, gave a 3.5 star rating out of 5, stating: "The whole Rat King story felt like a distraction to the whole Trubel-returns story, though in actuality it was (at some level) a branch of the same tree. The Reinigen apparently only become the Rat King when they are collectively terrified, which in this instance was almost certainly a symptom of the brewing Occultatem Libera uprising."[5]

Liz Prugh from EW wrote, "Renard is still being recruited by Andrew Dixon and his campaign manager for an endorsement from the Portland PD. Renard is still skeptical, but they bribe him with an offer to be police chief. What's the real play here? I'm sensing sketchy vibes."[6]

MaryAnn Sleasman from TV.com, wrote, "Grimm's last two seasons have been phenomenal in terms of world-building and storytelling, giving us a lush and detailed world full of exciting, mysterious, and fascinating cultures and dangers. I miss that. Season 5 has struggled to recapture that, coming so close at times only to fail with Gotham levels of instability and K-Mart quality. It's a frustrating series to watch these days because I know how good it can be, but this season has left me scratching my head after nearly every episode. What are you trying to accomplish, Grimm? What kind of bender did you go on over the summer hiatus that you're still such a hot, hot mess? This walk of shame has gone on entirely too long."[7]

Christine Horton of Den of Geek wrote, "There are still many questions left unanswered. What is Meisner's involvement with the uprising? Is he merely a gun for hire? Why was Trubel being held captive – if she was at all? And how did she find Nick’s house in the first place?"[8]