At first, “Better Call Saul” was a very good series, if a rather pallid, slow-moving prequel to its sire, “Breaking Bad.” In season two, the AMC program has developed into two very good series in one, existing in the same, barely overlapping space — the saga of Jimmy McGill, Bob Odenkirk’s ethically challenged lawyer; and Mike, Jonathan Banks’ grizzled former cop turned part-time enforcer.

As usual, anyone looking for a lot of pyrotechnics out of the season finale (and SPOILER ALERT if you haven’t watched), co-written (with Heather Marion) and directed by Vince Gilligan, has misjudged “Saul’s” understated rhythms. But the show ended both of its parallel plots in rather tantalizing fashion, setting up another slow burn until the series returns — likely with another fleeting flash-forward of Saul, post-“Bad,” looking over his shoulder, before easing into its next phase.

Perhaps foremost, this season took two characters who exhibited sporadic promise in season one and made them far more interesting: Kim (Rhea Seehorn), who ultimately threw away a chance at partnership in a big law firm to try independent practice alongside Jimmy; and Chuck (Michael McKean), Jimmy’s eccentric brother, whose disdain for his sibling was neatly advanced throughout the year.

That included the devastating flashback that opened the final hour — as their mother gasped out her last breaths — and the closing flourish, in which Chuck tricked Jimmy into a tape-recorded confession, setting up a battle with potentially serious consequences that might finally explain how “It’s all good, man” became more than just a slogan for Bob Odenkirk’s character.

For all that, the Jimmy plot was frequently overshadowed throughout the season by Mike’s, with Banks enjoying a much-expanded role and the show benefiting accordingly. Mike’s need for cash to help support his daughter in law and granddaughter has put him in contact with some very, very bad people, while consistently testing the outer regions of the world-weary detective’s moral compass. Not surprisingly, Mike’s descent into darkness, despite a different starting point, already exhibits notable parallels to that of “Bad’s” Walter White, with each choice feeding into the next, almost like slowly stumbling down a flight of stairs.

Saul’s name might be in the title, but this is every bit as much Banks’ showcase, and overlooking his wonderfully restrained performance come Emmy time would be more of a crime than anything Mike has done, either in the last show or this one. Indeed, the beating he took from Tuco (Raymond Cruz), in an effort to get him off the street — working on behalf of Nacho (Michael Mando) — was likely the season’s most memorable moment.

Like Jimmy, Mike’s story line ended with a very sizable loose end. After flirting with gunning down the drug lord who has crossed his path (in a scene positively fraught with tension, down to the ambient sound), Mike was warned off the hit, with a blaring horn and cryptic note, “DON’T,” left on his windshield.

The challenge for prequels, inevitably, is to remain connected to the source material without chewing through plot so fast as to run out of operating room — or, conversely, so slowly as to lose narrative momentum and thus interest. While it wasn’t entirely clear at the outset “Better Call Saul” could completely master that delicate balancing act, the second half of its opening frame and the twists in season two suggest this concept has plenty of gas left in it (especially served up in 10-episode increments) before reaching either of those junctures.

“Breaking Bad” remains a one-for-the-ages-type show, and “Saul” hasn’t reached those heights. But given the evolution of its birth — from what was supposed to be a half-hour comedy into the more ambitious beast it became — in terms of any admirer of the original making the time to watch it, that one-word note on the windshield would simply read, “DO.”