By Carolyn Hayes

Imprudent as it may seem to turn up the small-town Texas heat at the sweltering height of summer, Williamston Theatre is confidently tripling down on the practice. The company’s seventh season closer is also the final installment of what it has dubbed the “Tuna Trilogy”: Following on the momentum of 2011’s “Greater Tuna” and 2012’s “Red, White and Tuna,” now the show hits the road in “Tuna Does Vegas” (by Jaston Williams, Joe Sears, and Ed Howard). Director Quintessa Gallinat takes the helm of the franchise in this installment, which heralds the return of stars Aral Gribble and Wayne David Parker. But against a deliberately kitschy comic premise and the goof-off tendencies of summer, the production is nevertheless operating at full firepower, staying notably high-concept to set off the script’s affable low humor.

Once again, Gribble and Parker assume the many characters running around rural little Tuna, Texas, from the gossipy radio deejays to the man-hungry diner waitresses and everyone in between. Most of the top Tuna favorites are represented, which introduces the serial-specific problem of finding new ground to cover. In such cases, popular choices are to introduce new faces or drop the familiar ones into a new environment; “Tuna Does Vegas” opts for both. Specifically, when radio personality Arles Struvie (Gribble) discusses his vacation plans for a Las Vegas vow renewal with his fussy wife, Bertha Bumiller (Parker), most of the town is incited to make the trek – despite not being invited.

Much of the first act, which is essentially confined to Tuna, sets the machinery in place for the various characters to decide on and prepare for the trip. By intermission, they’ve left the little ol’ homestead behind and made their way to the dazzlingly garish Sin City. Despite a reserved few cosmetic alterations in Bartley H. Bauer’s set, the change in atmosphere is like night and day, helped by auditory and visual excesses courtesy of designers Genesis Garza (lights) and Will Myers (sound). This still may be the desert, with its anonymous sand-colored decor, but it’s definitely no place like home. The effects are wild and wonderful, just what the script ordered to shake up these small-town types and throw them out of their well-traveled depths.

Once in Vegas, the audience is introduced to a few new faces and scenarios, including – what else? – a pair of professional Presleys. A particular highlight is Gribble’s sinus-abusing hotel proprietress, who makes a game out of bilking her guests at every conceivable turn. Similarly wondrous is the up-and-coming hotel floorshow, which is too rich to spoil, except to commend Karen Kangas-Preston’s costume work for hitting the gaudy jackpot.

Yet the more things change, the more they stay the same: While the material can be hit and miss at times (and really, how many sequels successively improve on the original?), this show’s most successful comic beats reside in the hilarious chasm between what people practice and what they preach.

The vicious animosity between superstitious Aunt Pearl (Parker) and virtuous society captain Vera (Gribble) is heightened when they’re trapped in close quarters together, but what makes it work is the straight-faced sanctimony of the performances. In the same vein, the romantic connection between lovebirds Arles and Bertha is unparalleled; it’s a spectacular (and spectacularly odd) relationship within which the heart of the silly story can sweetly roost.

With its built-in emphasis on character, any “Tuna” is only as good as its citizens, and the duo of Gribble and Parker is as marvelous as ever. On the one hand, this team will go to any lengths for a laugh, indulging in gawky and gross do-it-yourself sound effects and playing up conventions of femininity. But on the other, they’re constantly elevating the material: They sail past obvious jokes for loftier payoffs, and their solid and expansive character work never feels reductive or cheap.

Granted, “Tuna Does Vegas” does fall victim to sequel problems, running a bit long with material that starts to feel a little lean. But with collaborative design and polished comic performances like these, it’s a treat to have another go-’round with this circus, far preferable to none at all. Viewers who caught the prior productions will need little coaxing to see this company bring its A game once again, and those who didn’t have one last chance before this superlative “Tuna” is wiped off the map.