The cast of “Decades” from the Capital Fringe Festival. (Courtesy 4&9 Productions)

Ready to time-travel? 4&9 Productions’ “Decades: A neat-o, far out, psychedelic, totally tubular improv show” takes unscripted theater to the 1950s, ’60s, ’70s and ’80s. Sadly for nostalgia-minded comedy lovers, the conceit never quite reaches light speed.

Ideas for each show — part of the Capital Fringe Festival — come from the audience members, who are invited to choose a family-friendly topic of conversation and an occupation that attracts men and women. The winning entry is picked out of a suitcase, and nothing is scripted. So each performance will be different, and future iterations might feature more promising prompts than “outdoor activities” and “sales.”

In the group’s first performance Saturday night, solid laugh lines were sadly scattered, with jokes tending toward the cheesy. (“Vocation? I’ll take you on a vocation, anywhere you want to go!”) The stretches in between never built up to a compelling plot. A nice thread about women in the workplace wound its way through some scenes, but it was overwhelmed by random references to bowling, disco and environmentalism.

Improvisational comedy is a high-wire act. Just avoiding dead air for a solid hour is an accomplishment, especially in a theater as overheated as the Gearbox, a tiny stage squeezed in above the Passenger bar. The cast is more than game, and there were plenty of bright spots. Katie Dunn stood out as a bossy hippie in the ’60s and an amorous personal assistant in the ’80s. So did Thomas Beheler as a ’60s professional looking to expand his mind, a ’70s cookie salesman and an ’80s show business intern. Jennifer Crawford, featured only in bit parts, was an invigorating presence every time she came on stage. The best scene of the night featured all three smoking weed in a park (in the ’60s, of course). Costumes were also a high point, with suits that ran the gamut from British Invasion velvet to disco leather to glam rock spandex.

The show-ending improvised song also was a highlight. Inventing with a musical number on the fly is even more of a challenge than standard improv. Here the risk pays off with a flight of fancy that’s truly transporting. “Decades” will play four more times through July 27. Visit