When “Person of Interest” — essentially CBS’ “Little Engine That Could” for the past four seasons — begins its fifth and final season tonight expect more of what has made the show increasingly bright over the years.

“The real fun of this season was that even though we had a reduced episode order it became kind of freeing creatively,” says executive producer Greg Plageman. “Jonah (Nolan) and I made the decision that if this was it, let’s go for it and let’s write to it.”

If you aren’t familiar, “Person of Interest” is about a reclusive and genius programmer, Harold Finch (Michael Emerson), who builds an AI that can identify crimes in advance, “Minority Report”-style. With the help of ex-assassin John Reese (Jim Caviezel), the duo work to stop crimes from happening. As the show progressed, it moved less from a procedural case (or number) of the week show to a more serialized format, while adding new characters to the team including reformed crooked cop Lionel Fusco (Kevin Chapman), lethal and emotionally distant assassin Sameen Shaw (Sarah Shahi) and the deadly hacker Root (Amy Acker). As the show evolved, a passionate core fanbase emerged from the woodwork.

“I was actually really surprised by our fanbase,” Plageman admitted. “I had no idea there was that much passion and fervor. I think part of it is the show always felt fresh and in many cases five minutes ahead on things. As people watched the show, what originally felt like science fiction became science fact.”

As for what to expect Season 5? With the Machine being reduced to a fraction of its former self, Finch, Root and Reese on the run from the enemy, and Shaw already in the hands of said enemy, don’t expect the momentum to be lost or the show to pull any punches for its swan song.

“I don’t think I’ve ever written a happy ending,” Nolan said with a laugh, when asked what hope there was for the team. “We’re not keen on happy endings here. Way back in the pilot, Finch promised that ‘this will end messily for all of them’ and I think we fulfilled the mandate.”

Whether or not the final season brings tears of joy or tears of sadness, Plageman stressed that these final 13 episodes were for their fans.

“It’s been a long time our fans have been waiting for this season and I can’t wait for them to watch it,” he said. “I think they’re going to feel really rewarded.”