Uniting Chicago Med, Chicago Fire and Chicago P.D. on one night brought One Chicago closer together than ever before. No longer airing on separate nights, the barriers between the Windy City-based procedurals have all but disappeared allowing for Dick Wolf's roster of colorful characters to freely move between the different shows. Wednesday night's tense episode of Chicago Med, titled "The Poison Inside Us," took full advantage of this stronger connectivity and saw several familiar faces from Fire and P.D. drop by for special assistance. Plus, the thrilling hour also featured the return of someone we haven't seen since Season 1.

It all went down when a belligerent man, who blamed Ethan (Brian Tee) for his wife's death, held the doctor hostage with a mysterious canister of toxic gas in an empty emergency room. Unable to calm the distraught man down, Ethan tackled him and accidentally unleashed those dangerous fumes into the air. The stunning event sent the ED into disaster mode with everyone quickly evacuating except for Connor (Colin Donnell) and Ava (Norma Kuhling) who couldn't risk their patent's life by moving him. Thankfully, Connor's nifty hybrid OR came with a special ventilation system that kept them safe from the toxic spill. Natalie (Torrey DeVitto) and Dr. Charles (Oliver Platt), on the other hand, weren't so lucky and the pair found themselves stranded on an empty floor with a patient in dire need of an emergency C-section.

With the hospital cleared out, Fire's Chief Boden (Eamonn Walker) and P.D.'s Upton (Tracy Spiridakos) dropped by to let Goodwin (S. Epatha Merkerson) know authorities were working on detoxing the scene and figuring out what poison was released in the ED. Crossovers were bountiful as P.D.'s Jay Halstead (Jesse Lee Soffer) also popped up to chide Will (Nick Gehlfuss) for undermining their investigation by admitting Ray. Plus, Fire's Cruz (Joe Minoso) showed up in a blue hazmat suit to reassure Connor that his crew was working on getting them out soon. I don't know about you but I can get used to these frequent mini crossovers.

Tracy Spiridakos and Eamonn Walker, <em>Chicago Med</em>Tracy Spiridakos and Eamonn Walker, Chicago Med

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Meanwhile, Ethan, despite inhaling whatever dangerous fumes were in the canister, insisted on helping other patients and shot down his colleagues' futile attempts to care for him. But in true Med fashion, Ethan's condition suddenly worsened and he dropped to the floor like a bag of bricks. With his life now hanging in the balance, April took matters into her own hands ran back into the contaminated ED--Herrmann's (David Eigenberg) pleas be damned--to retrieve medicine that could help her ex-boo. Her efforts earned some harsh words from Will who told her, "That was incredibly stupid." But it was all in the name of love so it's okay, right?

Elsewhere, Charles put on the show of his life after realizing he had no cell signal and therefore was unable to call someone to talk Natalie through an emergency C-section. Pretending that another doctor was on the line, he walked her through the first steps of the process and forced Natalie to trust her instincts in order to get her patient's baby out safely. Charles' plan may have worked but Natalie did not enjoy being tricked into such a risky procedure without any real backup.

While Natalie remained composed under pressure, Will found himself buckling under the weight of his secret gig as a criminal informant. Stress-related ulcers landed Will in a hospital bed with a worried Natalie asking him if everything was alright. But Will, unable to spill the beans just yet, remained tight-lipped. The stress might be getting to him but for now, he's keeping mum on his new side job.

Med's hectic day wrapped on a high note with Ethan, who was poisoned with cyanide, on the road to a full recovery. However, his relationship with April may have just flat-lined despite the pair still harboring serious feelings for each other.

Relieved that Ethan is going to be just fine, April was on her way to check in on him but stopped dead in her tracks when she realized he already had a visitor: his old flame Vicky Glass (Cynthia Addai-Robinson), who we haven't seen since Season 1. She's been back in town for months and unfortunately for April, might be sticking around for now. It looks like Ethan and April's road to reconciliation just hit another bump.

Chicago Med continues Wednesdays at 8/7c on NBC.

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Brian Tee, <em>Chicago Med</em>Brian Tee, Chicago Med