On a Wednesday evening in July, members of Island groups the IMPers and the newly re-formed WIMPs walk through Grange Hall in West Tisbury seeking that proof of spontaneity which is customary to any improv show: suggestions from the audience.

“We need a playwright,” they say.

Confident he has the perfect answer, a little blond-haired boy shoots up his hand and yells, “Harry Potter!”

The performers accept Tennessee Williams, but the kid fights on.

“A musical?” Harry Potter.

“Actor?” Harry Potter.

“T.V. genre?” Harry Potter!

The performers eventually add the boy’s suggestion to the rest and draw up a scene at Tony’s Market in Oak Bluffs, a tale of difficult customers.

They repeat the scene, adding in twists as the crowd suggests them.

They crouch and snap when the crowd suggests a West Side Story spin on it. They mutter awkwardly for Woody Allen, play it overly dramatic for soap opera and, yes, brandish their wands and English accents for Harry Potter. The audience of mostly children and parents soaks it up with squeals of laughter.

After a four-year hiatus, the WIMPs are back. Returning college students Ed Cisek, Ashley Peters and Devin Colter have reincarnated the well-known improv group that performed around the Island for 10 years before ending their last regular season in 2004. With the help of the IMPers, their high-school counterparts, and director Donna Swift, the returning students are continuing a 14-year tradition of weekly improv shows, every Wednesday at 8 p.m. in Grange Hall.

For the new WIMPs, it’s like dusting off the cape of a retired superhero.

“I used to idolize the WIMPs,” says Mr. Cisek, a rising sophomore at De-Paul University. “It was the first improv I had ever seen, so it means a lot to me now that I’m one of them.”

By bringing back the WIMP name, Mr. Cisek says he, Ms. Peters and Mr. Colter have tapped into the group’s rich history and Island-wide name recognition.

The WIMPs started in 1994 as a group of young performers who had majored in theatre and were looking for an outlet on the Island. Ms. Swift, a one-time performer with the group, now teaches the IMP program and directs the IMPers, her professional teen troupe. The IMPers and WIMPs perform as a single group, just with different shirts.

Before the show, Ms. Swift sits in the middle of Grange Hall, scrutinizing the cultish chants and claps of the warm-up exercises. While the performers drift across the stage emitting noises and words seemingly snatched from the summer air, she shouts pointers and drills like a football coach.

“Connect and commit!”

“You guys know you’ve gotten sloppy on articulation.”

“Bigger, huger, bigger, huger. I see doubt!”

These warm ups, members of the group say, are a pre-show ritual in which they attempt to tap into something they call group mind.

“It’s the theory that there’s this controlling force that connects us,” Mr. Cisek says.

The performers stand in a circle with their heads bowed, moments before the show opens.

“Just focus on each other,” Ms. Swift instructs, walking around the circle. “Connect into the group mind and the rest will take care of itself.”

Unscripted and unrehearsed, short-form improvisation is never the same way twice. Anything can happen and it’s often hit or miss. When it hits, it’s pure comedy. When it misses, unflinching, it moves on.

“I used to get so scared before shows,” says Ray Ewing, an IMPer and rising senior at Martha’s Vineyard Regional High School. “I’ve been improvising with these kids for years and now it’s so comfortable, like having a conversation.”

Wednesday night improv performances at the Grange Hall continue weekly through August 20. Tickets are $11 at the door. Shows begin at 8 p.m.

On Monday nights in August, members of the group also will improvise longer one-act plays at the Katharine Cornell Theatre in Vineyard Haven.