The Thinker lays a trap for Barry that he can't outrun, setting up a new and interesting dynamic for when The Flash returns next year.
WARNING - This review contains SPOILERS for The Flash season 4, episode 8.
The Flash season 4 has been a return to form, recapturing the lighter tone of the show's first season with humor and callbacks to those early days. Since returning from the Speed Force, Barry has been re-energized and happier than ever. His friends are safe, his family growing, and after defeating the Nazi invaders from Earth-X in last week's Arrowverse crossover, Barry and Iris were finally married. Life is going well for Barry, which is why it's time The Thinker taught him a valuable lesson: "There are no happy endings."
"Don't Run", season 4's midseason finale, brings The Thinker's evil scheme back in to focus, seamlessly connecting the two plots running through this episode with the overall storyline of the season. Both threads in this episode involve a member of Team Flash being kidnapped - Barry by The Thinker, Caitlin by Amunet. And at first, neither of these incidents appear to be connected, but they are each a fundamental step in The Thinker's plan to not only save his own life but ruin Barry's happy ending.
While out shopping for Christmas presents, Barry and Iris are set upon by The Thinker, who snatches Barry with his chair's robotic arms and flies off. (It's just as ridiculous looking as it sounds.) When Barry comes to he's a prisoner inside The Thinker's sanctuary, where Devoe lectures him as only as a villainous college professor can. The two share that quintessential hero/villain banter until, eventually, Barry escapes his prison. The Flash and The Thinker then do battle, with Barry hanging on for dear life as Devoe whizzes around the city skyline in that flying chair. (Again, it's looks ridiculous and the whole sequence is a distracting bit of CGI pushed beyond the limits of a TV budget.) In the end, both of them plummet into the river below - with that flotation mode Cisco installed in Barry's suit finally paying off - and while Barry comes ashore, Devoe is nowhere to be found.
It's a pretty cut and dry plot line that seemingly goes nowhere, but it's merely a distraction for what The Thinker is really planning. There's even an instant where it seems like Devoe will kill Joe West (heaven forbid), but it too is all a part this grand misdirection.
While Barry is The Thinker's prisoner, Caitlin is held captive by Amunet - the criminal mob boss Killer Frost worked for as a hired gun. The reason Amunet has come for Caitlin and not Frost is that she needs her medical know-how to safely remove a shard of metal she's accidentally wedged in the head of the meta-human The Thinker hired her to collect. With Amunet threatening to kill her if she can't save the meta's life - a young man named Dominic who's developed the ability to read minds - Caitlin is forced to use her own cleverness to escape and save them both.
And at first this feels like the episode's B-plot, allowing Caitlin to make the case that she's just as useful as Killer Frost in spite of her teammates sharing how much they enjoy her alter-ego's company. It's a good bit of character work, reminding audiences that Caitlin has been a valuable member of Team Flash long before she developed her super-powered split personality. Frost is sure fun (BAKING SODA!), but Caitlin's pretty great, too. Plus, having her play off of Amunet (who Katie Sackhoff continues to portray with a mad glee) makes for an engaging conflict, with Amunet being both an antagonist and a cheerleader, urging Caitlin to believe in her own abilities.
Caitlin is eventually able to orchestrate her and Dominic's escape, with Cisco and Ralph arriving for the last-minute rescue, but this is by no means where the story ends. Assuming the day is saved, Team Flash resumes their search for Devoe and are oblivious when Dominic is kidnapped again by Amunet. She then successfully delivers him to The Thinker, who transfers his mind into Dominic's body.
This is where "Don't Run" gets real interesting, because not only has The Thinker successfully duped Team Flash and secured himself a new body, free of illness, he's also gained the perfect alibi by assuming Dominic's identity. Sure, like any smug villain, Devoe reveals to Barry the truth that the kind telepathic meta they rescued is now his new form, but it will be a tough pill for many to swallow - especially when combined with a cliffhanger that sees Barry framed for the murder of Clifford Devoe. This, too, is laid out brilliantly, with the murder scene composed perfectly in Barry's apartment and the act made all the more believable given his erratic and seemingly dangerous behavior towards Devoe.
When The Flash returns next year, Barry will go to trial for Devoe's murder in what is yet another strong callback to season 1, mimicking the wrongful imprisonment of Barry's father for his mother's murder. It's an interesting development that absolutely derails any chance at Barry and Iris having their happy ending. Luckily for him, Iris gained even more confidence in her leadership (thanks to a little pep talk from Harry) and should more than ready to support and fight for her husband. The Devoes may have won this round, but the West-Allens aren't finished yet.
The Flash season 4 continues on January 16th, 2018 on The CW.