Chicago Fire's Casey Discovers a Gruesome Scene in One Chicago Crossover Sneak Peek

This year's One Chicago crossover feels like the zombie apocalypse. In an exclusive sneak peek at the three-way event, which airs Wednesday, Oct. 16 on NBC starting with Chicago Med at 8/7c, the Windy City's embattled first responders discover a gruesome scene while hanging out at a Chicago Bears game.

In the preview, Chicago Fire's Casey (Jesse Spencer) sees a young man collapse outside of the football stadium and immediately alerts the rest of the crew, which includes Severide (Taylor Kinney), Brett (Kara Killmer) and Kidd (Miranda Rae Mayo), Chicago P.D.'s Upton (Tracy Spiridakos) and Burgess (Marina Squerciati), and Chicago Med's Dr. Manning (Torrey DeVitto). However, the stable situation takes a serious turn when Manning discovers a gnarly infection on his leg. With no idea what is causing the victim's limb to look like something about of an Eli Roth movie, the gang may have stumbled onto their biggest and most baffling case yet.

The three-hour event, titled "Infection," will see Med, Fire and P.D. come together to figure out what is making the people of Chicago fall ill. The stakes are especially high since the suspected outbreak threatening the entire city is likely an act of terror.

One Chicago's annual crossover airs Wednesday, Oct. 16 on NBC starting with Chicago Fire at 8/7c, followed by Chicago Med at 8/7c and concluding with Chicago P.D. at 10/9c.