“Vikings” has been enough of a success for History that the channel not only expanded the number of episodes ordered per year but split them into “A” and “B” seasons, much like AMC’s pattern with “The Walking Dead.” But the messy, somewhat confusing midseason finale and indeed developing arc of this latest run — despite some first-rate moments — suggests that might have forced the producers to wring a little too much plunder out of the concept and characters.

For all the side plots, betrayals and intrigue in the ongoing quest for power within this medieval, historical world, the fourth season was dominated by the rift and inevitable showdown between the Viking brothers Ragnar (Travis Fimmel) and Rollo (Clive Standen), with the latter having settled among the French, and devoted himself to the defense of Paris. That built toward a siege and one of those brawny, bloody battles that the series has consistently mounted so well, as Rollo — well-schooled in Viking tactics — helped beat back his countrymen’s assault.

In the finale (and SPOILER ALERT) if you haven’t watched, Ragnar and Rollo finally got to make like Romulus and Remus and square off, brutally pummeling each other until both looked like Sylvester Stallone at the end of “Rocky” (1 or 2, take your pick). But the fight ultimately proved inconclusive, as Ragnar and several of his wounded companions were forced to engage in a rather hasty retreat, while Rollo was embraced and celebrated as the city’s savior.

So far, so pretty good, although one can argue that the focus on the two brothers this season came at the expense of some side plots. But then series creator Michael Hirst went straight from that into a rather sizable if ill-defined time jump, with Ragnar’s now-grown sons sitting around grousing about his extended absence, only to have dad conveniently waltz back into town, sporting an Odin-like beard and demanding that one of them step up and kill him to demonstrate that he’s worthy of becoming king.

Hirst is clearly betting that fans of the show have invested enough in this dense, gritty dive into Viking culture that they’ll stay faithful through the transition to Ragnar’s sons, paving the way toward “Vikings: The Next Generation.” Moreover, he has history (and for that matter, History) on his side, since Ragnar’s heirs eclipsed him, including his son Bjorn (Alexander Ludwig).

Nevertheless, the closing portion of the episode felt mostly unsatisfying, with no explanation regarding Ragnar’s disappearance or return, and a bit of disorientation about the kids (now played by older actors) and what transpired during the intervening years. All that will surely be fleshed out when the program returns, but for now, the finish didn’t conjure any special enthusiasm about starting over with Ragnar’s progeny, if not exactly hitting the reset button.

Of course, “Vikings” has already bucked long odds, establishing a loyal following on a channel with scant profile in the scripted arena — and certainly in series — when it made its debut (as something of an afterthought to “The Bible”). That said, History has put a lot of eggs in this basket, and to an extent, after the time spent getting to know the existing characters, this latest scenario feels a little too much like Lucy pulling the football away from Charlie Brown.

That’s not to say “Vikings” won’t merit another look when it comes back, if only to gain a clearer sense of where the story goes after boldly opting to shuffle the deck in this manner. But having sailed into Season 4 with what felt like the wind at its back and considerable promise, suddenly the waters ahead — and the show’s prospects — appear far more turbulent.