The San Francisco Mime Troupe’s new outdoor summer musical “Walls” is about a “criminal illegal alien lesbian with mental health issues who is in love with an immigration agent.”

At least, that’s the over-the-top description by Breitbart, which recently posted a rant about the grant money the Mime Troupe, with its suspicious red star logo, receives from the National Endowment for the Arts.

Zaniyah (Marilet Martinez), one of three immigrant characters featured in “Walls,” has indeed crossed the border illegally from Mexico, and has a touch of post traumatic stress disorder from the horrific journey through the desert.

But she is neither mentally ill nor criminal-minded: She is simply a young woman desperate for work to support her poverty-stricken family back home in their drought-ridden, polluted village.

Stuck in a sort of limbo on the American side of the border, she is in love with Immigration and Customs Enforcement agent Mary Jones (the invaluable Velina Brown), a military vet struggling to come to terms with her job responsibilities and her conscience.

When Zaniyah gets hired by a Somalian Muslim immigrant grocery store owner (Rotimi Agbabiaka, himself a Nigerian immigrant here, and an impressively transformative actor), and when another ICE agent, an Irish immigrant-turned-super-patriotic-American-citizen named, challengingly, Cliodhna Abhabullogue (Lizzie Calogero), sets out to capture a terrorist or two, tensions rise.

In humanizing all of the characters, including government agents and even Mary’s racist fisherman father (Agbabiaka again), and in including voiceovers of recent past presidents (as well as the current one) describing their plans for controlling the border, “Walls” examines an ongoing and fraught national issue from various angles.

One character wonders what it would be like if there simply were no borders around the country.

If “Walls” is one of the Troupe’s most straightforward, and perhaps least wacky, comedies, that seems fitting for these uneasy times.

But there’s still plenty of humor in Michael Gene Sullivan’s script and in the finely tuned commedia-style antics of the four-actor ensemble.

Part of the fun of a Mime Troupe show is the music; “Walls” includes catchy songs with lyrics by Piero Amadeo Infante and music by Michael Bello, with the three-person SFMT band also underscoring the action.

A topic like this one is no laughing matter, but with Sullivan’s wit, and the talents of this excellent cast under Edris Cooper-Anifowoshe’s fast-paced direction, the Mime Troupe strikes just the right balance between comedy and — for too many in this country of immigrants — tragedy.