Chicago Fire Chicago Fire

The Firehouse 51 team has battled all kinds of fires and disasters on Chicago Fire this season. However, it seems the producers have saved the biggest, and best, blaze for last.

"For the first time this season, Firehouse 51 is going to face a harrowing episode-long rescue call that will affect them all collectively," executive producer Danielle Gelber tells of Wednesday's season finale (10/9c, NBC). "Our season finale is going to be chock-full of cliff-hangers across the board. We're going to leave everybody in some intense state of unrest."

Add the new fall shows to your watchlist

This last rescue call marks the end of a banner first year for the NBC drama. In what was otherwise a tough TV season for the network, which canceled seven other freshman series earlier this month, Chicago Fire

has slowly grown into one of NBC's surprise hits. Since its October debut, the firefighter drama has become an hour of must-Tweet TV and spawned a spin-off, Chicago PD. So how did it happen? Here are five secrets to Chicago Fire's success:Make viewers invested: Dick Wolf's Law & Order paved the way for the modern-day television procedural, with its focus on the intriguing, twisty cases of the week, rather than the cops and lawyers working on these cases. More than 20 years later, that playbook has been tossed out. "It's very diametrically opposed to what he succeeded with in the past, but I knew that in this day and age, what people really come back for every week is the people, the characters," Gelber says. "We've tried really hard to weave the characters' emotional lives and their relationships into their daily work. They never really go on a call that doesn't somehow resonate with what's going on in their personal lives."

TV's sexiest crime fighters

Don't be afraid to go too far:
Hookups, breakups, babies, blackmail, death. It feels like Casey (Jesse Spencer), Severide (Taylor Kinney) and the rest of the crew have been through way more than just one season's worth of drama thanks to fast-moving, unpredictable story lines for all of the characters. That pace has kept viewers hooked week after week, and producers aren't slowing down. "We're not worried. We have so many stories to tell," Gelber says. "This is such a rich tapestry of characters that we're just so excited to be able to go even deeper next season. I don't think we'll have any shortage of personal stories to tell on the show." Don't expect the fires to cool down anytime soon either.  "We've got one of the most incredible consultants for the rescue call side of it, so we will always be able to find some great human rescue stories to tell as well," she adds.

Embrace the future: It's these characters and their roller-coaster personal lives that have made Chicago Fire not just a solid performer for NBC, but also a bona-fide social media hit. Every Wednesday night at 10/9c, thousands of fans are tweeting about the episode and whether they're #TeamSeveride or #TeamCasey. "Social media has had so much to do with our success. Our audience is so deeply invested in the character relationships that Facebook and Twitter and even Instagram ... give them all extra outlets to share their thoughts and their emotions about the show on an ongoing basis way past the hour that it's aired," Gelber says. "We really watch for it because the future is now. We have to embrace it. It's a huge advantage to us."

This season's MVPs

Give the fans a voice:
Producers have also been keeping their eye on Facebook and Twitter all season to see just which story lines and pairings are hitting the deepest nerves with fans. Gelber says the fans are a big influence for the show's direction. "I have always thought of television as a living experiment. As you're making it, you're seeing what's working with audiences, who it's speaking to, and you write towards that absolutely," she says. "We have found that certain pairings really work because of great casting chemistry ... and we write towards those." Gelber points to the tight friendship between Severide and Shay (Lauren German) as an example, as well as the heated love triangle between Casey, Dawson (Monica Raymund) and Mills (Charlie Barnett).

Always think ahead: Not only did Chicago Fire earn a renewal, but it's also one of the youngest shows to earn a spin-off. Days before the planted Chicago PD spin-off aired last week, NBC ordered the series to premiere sometime next year.  "NBC has been incredibly supportive of the show from minute No. 1 and there was always some background long-term thinking that if Chicago Fire works, there's more story to tell in the city of Chicago," Gelber says. "There's always the medical world and politics and many other things. But we were really don't want to get ahead of ourselves. We want to focus on making Chicago Fire the best second season hit we can possibly be." The writers have already started work on planning out Season 2. "Our writers have been completely immersed in what's going on for next season," Gelber says. "They've thought long-range about where we're going to take everybody next season."

Chicago Fire airs Wednesday at 10/9c on NBC.