Opening quote: "Catch me when you can..." A string of homicides has the press asking Captain Renard if a Jack the Ripper copycat has arrived in Portland. Monroe traces the mode of operation of the homicides to the Luxembourg Peasants' Revolt. While dealing with the investigation, Nick, Hank, Monroe and Wu deal with a situation they never expected. Meanwhile, Adalind and Rosalee must work together on a last-ditch attempt to fix Juliette's condition. Elsewhere, Juliette decides to help her new ally even if it means hurting those around her.
Reception
Viewers
The episode was viewed by 4.22 million people, earning a 0.9/4 in the 18-49 rating demographics on the Nielson ratings scale, ranking third on its timeslot and eight for the night in the 18-49 demographics, behind 20/20, Dateline NBC, The Amazing Race, Hawaii Five-0, Blue Bloods, Beyond the Tank, and Shark Tank. This was a 10% decrease in viewership from the previous episode, which was watched by 4.66 million viewers with a 1.0/4. This means that 0.9 percent of all households with televisions watched the episode, while 4 percent of all households watching television at that time watched it.
Critical reviews
"You Don't Know Jack" received positive reviews. Les Chappell from The A.V. Club gave the episode a "A-" rating and wrote, "The fact that the showhas gonethe distance it has in reversing the roles of the two women is a large part why Grimm now feels like it's growing in the right directions. After 'Iron Hans' burned down literal and metaphorical links to Grimms past, 'You Don't Know Jack' doubles down on those moves by further pushing Adalind and Juliette into their opposite camps. And for the second week in a row, those moves feel like the right moves, as it's another exciting and captivating episode that's a cut above most of what's come yet this season." Kathleen Wiedel from TV Fanatic, gave a 3.8-star rating out of 5, stating: "Prince Kenneth is too smug for his britches, that's for flaming sure. He easily manipulates Juliette into doing exactly what he wants, where he wants. Creep. Every time he opens his smarmy mouth, I imagine the comeuppance that I dearly hope is coming his way. Kenneth's plans play a significant role in GrimmSeason 4 Episode 20, but a surprisingly interesting Case of the Week and digging up Adalind's mother drew my attention away." MaryAnn Sleasman from TV.com, wrote, "Can we agree that just handing the Hexen-juice over to Juliette in her current uncooperative incarnation and expecting her to drink it without argument was so utterly naïve on the part of Nick, Monroe, and Rosalee that the only rationale I can come up with for their utter stupidity is that there are still two episodes of Grimm left this season and they need to keep the crazy-Juliette gravy train going just a little bit longer." Christine Horton of Den of Geek wrote, "The writers have hit the pedal with some force, with 'You Don’t Know Jack' taking a surprisingly sinister turn, as well as delivering some proper shocks. However, this episode provided a couple of genuine 'what the hell?' moments that could signal big changes for the course of the show. Conversely, it was also one of the funniest episodes in a while, with Adalind taking the lion's share of pithy one-liners."
