As an agitprop musical theater collective, the San Francisco Mime Troupe has to put a lot of thought into which pressing issue to tackle for each year’s free show in the parks. This time around, in the company’s 58th season, it seems like there’s a plentitude of villainy afoot to rally the citizenry to resist.

Troupe resident playwright Michael Gene Sullivan’s latest musical satire, “Walls,” takes aim at immigration crackdowns. That’s certainly been a huge talking point for the current administration, though the play is peppered with sound clips of “nation of immigrants, but a nation of laws” rhetoric from the past few presidents to illustrate that it’s not a new one.

L. Mary Jones knows her job. A longtime agent with U.S. Immigration and Customs Enforcement, she’s more than prepared to be tough as nails to make sure people coming here to build a new life have their papers in order or go back where they came from. The trouble is, her girlfriend, who lives with her, is an undocumented immigrant, so Mary has to go to great lengths to avoid taking her work home with her.

As usual in recent years, the play is performed by a tight cast of four playing multiple roles. Velina Brown mixes a take-charge attitude with nagging doubts as Mary, who’s pulled between her sense of duty on one side and her love and compassion on the other. (Lauren Spencer has since taken over the role) But Mary has it easy compared to her girlfriend, Zaniyah (sympathetically anxious Marilet Martinez), who frets about finding work and being discovered, and who’s severely traumatized by her border-crossing experience. In fact, every time she starts to say the word “border” she starts convulsing to the sudden cacophony of the band.

Rotimi Agbabiaka is amiably chatty as Bahdoon, a friendly Somali American shopkeeper, and also pops up as a barking ICE supervisor and as Mary’s eccentric shrimp fisherman father ranting about “illegals.” As soon as he shows up, you just know that the perfectly legal immigrant Bahdoon, a practicing Muslim, is going to get scapegoated for something.

Lizzie Calogero is an overzealous true believer as the unpronounceable Agent Cliodhna Abhabullogue, an Irish immigrant ICE agent itching to bust some huddled masses yearning to breathe free. The heavily accented Agent Abhabullogue considers herself ultra-American and anyone who doesn’t look like her to be interlopers, but of course her own reasons for coming over to the fabled land of opportunity were pretty much the same as the people she’s hunting, as she’s reminded by a ragged leprechaun played by Martinez in an amusingly weird interlude.

A former performer with the company, director Edris Cooper-Anifowoshe gives the play a brisk staging of less than 80 minutes in her first Mime Troupe show since 1991. With lyrics by Piero Amadeo Infante and music by Michael Bello, the songs are more dynamic than usual, from Zaniyah’s cabaret “Lamento” to Bahdoon’s upbeat Afrobeat ode to the “Land of Milk and Honey” and Abhabullogue’s gloating hard rock anthem “Don’t You Wish You Were American.” Carlos Aceves’ evocative set depicts a disassembled Statue of Liberty, the inconvenient symbol of a welcoming nation of immigrants.

The show has a lot of funny moments but is ultimately sobering, with a downbeat ending and not much hope for positive change aside from a general reminder to know your rights and fight for them. Sometimes the change that’s needed has to start in hearts and minds before it can make a dent in the system.