"The Sisters Mao," Gavin McCrea's second novel, is a stirring, perceptive exploration of radical politics. Two of the Irish writer's protagonists, sisters Iris and Eva Thurlow, are among a small number of disaffected Londoners who live together in a shuttered warehouse. A look at the walls affirms the group's shifting loyalties.

Posters of Che Guevara and Fidel Castro have grown tattered, but an image of China's merciless dictator is bigger and "less ragged." It's 1968, and the counterculture has a new hero in Mao Zedong.

As he demonstrated in "Mrs. Engels," his brilliant debut, McCrea is particularly interested in the growth of left-of-center movements. At 500-plus pages, his follow-up is a sweeping portrait of three women shaped by fanaticism, dysfunctional families, intra-group sexism and politics-as-performance.

Iris and Eva grew up in a liberal family of career-first theater types. They resent their parents' selfishness, and now, in their 20s, they're staunch nonconformists. Iris sells LSD. Eva leads an activist theater troupe. When French students stage huge protests against capitalism, racism and war, Eva heads to Paris to join the sits-ins. She returns to England weeks later, accompanied by several belligerent Maoists. Inspired by Mao's endorsement of revolutionary spectacle, the group plots an ugly public disturbance.

This story line runs parallel to one about Jiang Qing, Mao's real-life wife. The onetime actress runs China's national ballet, which is prepping its latest agitprop performance. Though internal Communist party dust-ups prevent her from seeing the dying Mao, Jiang Qing remains a tyrant in her own right. She sends a shopkeeper caught selling Western shoes to a brutal work camp. If dancers don't excel, she assaults them. A woman in a male-dominated movement, she's distinguished herself through sheer ruthlessness. "More radical even than my husband," she says of herself, "more Mao than Mao."

"The Sisters Mao" captures a particular moment in far-left politics, when Western supporters of the Soviet Union belatedly accepted the truth — that the USSR killed millions of innocents. Iris and Eva's cohort mock older liberals for blindly backing Josef Stalin, yet they too embrace a prolific murderer. Their professed love for Mao sounds like racist condescension. Chinese people are fundamentally "honest," says a European Maoist. "They get worked up over a little event and start crying. They're so sincere."

Like the real deal in China, the dilettanteish Maoists in England are prone to witch hunts. Eva's hardest-line comrades — swaggering men, all of them — badger their allies, "searching out errors in people's attitudes." When Eva's crowd learns that Chinese accused of dishonoring Mao are publicly humiliated, they think it's "wonderful, an effective technique of persuasion."

Unchallenged, dogma can metastasize, morphing into violent radicalism. This excellent novel, populated by maddening, memorable characters, offers a timeless reminder of extremism's perils.

Kevin Canfield is a writer in New York City.

The Sisters Mao
By: Gavin McCrea.
Publisher: Scribe, 560 pages, $28.