In the classic model for a cable TV drama, starting with “The Sopranos,” the penultimate episode of a season also serves as its climax, with the finale acting as a denouement. That hasn’t been the case with Season 3 of FX’s “Snowfall,” where back-to-back episodes explosively changed in the show’s narrative.

Episode 8 ended with crack kingpin Franklin Saint (Damson Idris) shooting LAPD cop Andre Wright (Marcus Henderson) in the head. Episode 9 ended with Wright’s daughter Melody (Reign Edwards) shooting Franklin in the back after her father’s funeral. She leaves him on the floor of her home, blood pouring out of his mouth.

Explains series co-creator Dave Andron, “We kept our foot on the gas the whole season.”

As Andre and Franklin were not only next-door neighbors but enjoyed a father-and-son relationship with Franklin’s dad out of the picture, these plot points will reverberate through the South Central LA community where they lived and where underground drug networks are taking over in 1984, when Season 3 ends, four years into Ronald Reagan’s first presidential term.

“Part of the story that we are telling is how … nobody understands how bad it’s going to get,” Andron says. “You’ve had Andre, who was in his captain’s office saying, ‘I think there’s a problem.’ They allowed him to orchestrate the [drug] raid, but it’s nothing like what it’s going to become when [crack] becomes national news.”

The other half of “Snowfall” concerns the CIA’s involvement in the drug trade, represented here by shady agent Teddy McDonald (Carter Hudson). His quest to fund the US war against communism in Central America — by making sure the flow of cocaine into LA doesn’t stop — is jeopardized.

“Teddy’s scrambling to try to keep his operation together,” Andron says. “I think the audience should be wondering, ‘Is Teddy fooling himself? How expendable is he? How important is he?’ ”

‘It was just a complete plague and a scourge … It wiped out a generation.’

As the show’s timeline enters the second half of the 1980s, things will become monumentally bleak. “I don’t know if you could pinpoint a moment between 1985 and 1989 when you could say [the crack trade] was at its absolute worst,” Andron says. “It was just a complete plague and a scourge. Part of what I don’t even think I understood when we started the show was what a massive turning point crack was for African-American communities. It wiped out a generation.”

Depicting Franklin’s demoralization has been a subtle undertaking for Idris, who, at 28, has become the face of the show. Andron reveals that the actor was not co-creator John Singleton’s first choice to play the role.

“He came to us through a tape,” Andron says. “I did have a heads- up that he was British, but I don’t think I would have known he was from the tape. His [American] accent was already incredible. There are people and certain movies that are taking a lot of heat for casting British-Africans as African-Americans. And we discussed it at length. John Singleton, rightly so, was initially very opposed to casting a British actor.

“We could tell that Damson was incredibly talented. There was kind of no disputing that, but he was so much better than anyone else. Once it became apparent that he was going to be able to put the show on the air, then it’s like, ‘Okay, then we have to do that and whatever heat we take, we’ll just deal with it.’ ”

Previews for Wednesday’s season finale show Franklin in some prison scenes (he has already served time for a lesser drug offense) and Andron, who will start up production on Season 4 after a vacation in northern Europe, is promising to deliver, he says, “a completely different episode than anyone would ever expect.

“I made a choice to go off and do something very different to help reset where we are in the life of this show, and the story we’re telling,” Andron says.

“Snowfall” Season finale 10 p.m. Wednesday on FX