LOS ANGELES — It's three shows sharing a single star, a place called Chicago.

"It's the backdrop to our city," 'Chicago Fire's' Jesse Spencer says, "But it's also the heart and soul of the show."

Patrick Flueger of 'Chicago PD' agrees. "Chicago's the main character of the show. We always say that."

RELATED: NBC's Chicago Fire, Med, and PD break new ground with season long story crossover

One thing 'Chicago Med,' 'Fire,' and 'PD' have in common is a never-ending quest for authenticity. For instance, Flueger based his character on an actual Chicago cop.

"He's an affable man, but you can't sneak up behind him," Flueger says. "It's like walking around the back of a horse. You got to let him know you're coming. Because if you don't, suddenly you'll be in an armbar. I've seen it." 

Yaya DaCosta of 'Chicago Med' has appeared on all the Chicago shows, including crossover specials that that carry a single story all the way through prime time, often against the backdrop of a ghastly disaster.

"Every crossover is going to be graphic," she playfully warns us. "Whenever you hear 'crossover,' don't eat during it. Have dinner before or after."

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