The Flash goes through the looking glass in the biggest episode yet

Arrow crossover aside, there was no more anticipated episode of The Flash this season than the one which aired last night. Finally, Barry Allen (Grant Gustin) and the team at STAR Labs would step through the interdimensional rift to Earth 2 and go on the offensive against Zoom. As a premise, the episode had everything going for it, but in execution it fell just a little bit short. Here's how it all went down.

The episode opened with Allen racing around and chucking Dr. Harrison Wells' (Tom Cavanagh) newly designed grenades into the dimensional gateways scattered around Central City. He succeeded in closing 51 of those gateways, denying Zoom access to Earth 1 from alternate dimensions. The final gateway, leading straight to Earth 2, he left open for the assault — and as a way to return to Earth 1 once he'd succeeded in freeing Wells' daughter, Jesse.

Deep inside STAR Labs, Caitlin Snow and Jay Garrick (Teddy Sears) watch as Allen grabs Wells and Cisco by the scruff of the neck and leaps through the last gateway to Earth 2. The travelling effects, while fairly pedestrian as far as CGI goes, did include a lot of fan service including glimpses of John Wesley Shipp's Flash from the 1990s as well as the modern incarnation of Supergirl.

But, just as Allen and company make it through the portal it crumbles behind them. That leaves Snow and Garrick less than 48 hours to repair it before Allen and Cisco are trapped there forever.

On the other side of the looking glass Earth 2 is splendid. It features art-deco inspired cars and lithe architecture surmounted with neon and chrome, as well as a monorail that shoots around the city hundreds of feet in the air. The retro-futuristic theme was carried over into the costuming, but over the course of the episode the illusion began to break down. As it turns out hospitals and abandoned warehouses, as much a focal point of this episode as any other in the series, tend to look pretty much the same on Earth 2. By the end I had trouble telling one dimension from the other.

Allen, Cisco and Wells post up inside STAR Labs, planning to use Vibe's powers to quickly find Zoom and then break for lunch. But Earth 2, it would seem, vibrates at a different frequency than Earth 1, which means Vibe's goggles do nothing.

Allen, in a fit of impulsive inspiration, sees himself on the news. Here on Earth 2 he still works for the Central City Police Department. Sensing an opportunity he races off to fetch himself, then tasers himself and takes his own place on Earth 2. That gives him access to police records, where he can pick up Zoom's trail while Cisco fixes his shades.

Off to the PD he goes to find Detective West, who turns out to be Iris ... and his wife. There's an awkward moment where Allen's making out with his adopted sister, perhaps foreshadowing where their relationship is headed on Earth 1 ... or perhaps not.

So, if Joe's not a detective, than who is he here? A Jazz singer. And not a bad one at that.

Allen's mother is also alive on Earth 2, which leads to a touching scene where the two talk for the first time in years. The scene was one of Gustin's best, most genuine performances of the year.

Later that night Iris and Allen are at the club listening to Joe sing, when almost without warning Killer Frost (the Earth 2 doppelganger of Caitlin Snow) and Deathstorm (the Earth 2 doppelganger of Ronnie Raymond [Robbie Amell]) enter the story. A melee ensues and Joe is mortally wounded.

Joe's death sends Allen off the deep end. He goes back to Wells, still in virtual hiding at STAR Labs, and tells him the hunt for Zoom is off until he can help Iris get revenge.

Meanwhile, on Earth 1, a new metahuman named Geomancer (Adam Stafford) is on the loose. He's not really given much screen time during the episode, but it's clear that the police are powerless to stop him. The only person who can save Central City is Jay Garrick. Snow begs him to use Wells' Velocity 6 serum to regain his speed force, but Garrick hesitates.

That's when the Flash from Earth 2 finally tells Snow his secret. Not only has he used speed force enhancing drugs before, but the side effects are what is slowly killing him. Snow vows to make a new drug, free of side effects, and to help cure his illness. By the end of the show he's hopped up on Velocity 7 and able to scare Geomancer into laying low until next week's episode.

Back on Earth 2, Iris and her partner Floyd Lawton (played by X and better known as Deadshot on Earth 1) head off to arrest Killer Frost and Deathstorm. Cisco follows along, armed with a pistol he thinks can stop Frost in her tracks. There they learn that the metahuman pair aren't actually working for Zoom. They're working for Reverb — Cisco's incredibly powerful Earth 2 doppelganger.

The highlight of the episode, by far, was watching Reverb try and recruit Vibe to his side. "Are you Cloud-City-Vadering me right now?" Vibe asks, a pocketful of Twizzlers barely covering up his prescient t-shirt.

Another battle ensues, ending with Reverb and Deathstorm pounding away on Allen's semi-conscious body while Vibe and Iris look on powerless to help. That's when Zoom shows up, kills Reverb and Deathstorm for their betrayal, and takes off with Allen.

While the episode started out with great promise, it eventually devolved into the same storyline we keep seeing over and over again. It's another instance of Allen's impulsiveness getting the better of him. It's another instance of his emotional ties crippling him. It's another instance of his terrible decision making coming back to bite him. He is a character that simply refuses to grow or change in any way, and seeing him repeat the same mistakes is getting boring.

But there's still a chance to save this particular story arc, and to see Allen break out of his rut. We'll just have to wait until next week to see if the show's writers are able to pull it off.