Co-directors Ben Cotner and Ryan White (who was here last year with his excellent film "Good Ol’ Freda") arrived at SXSW with a healthy pedigree for this collaborative effort. It debuted earlier this year at Sundance and will be airing this summer as part of the HBO Documentary Films lineup. They spent five years chronicling the fight against California’s anti-gay Proposition 8, which was a voter-approved measure in 2008 that made same-sex marriage illegal in the state and invalidated about 18,000 marriages that had occurred during a brief window of time when it was legal.

Kristin Perry and Sandra Stier, a lesbian couple who had been together for a decade and have four sons, joined Paul Katami and Jeffrey Zarrillo as the plaintiffs in a lawsuit to challenge the proposition in 2009. This fly-on-the-wall documentary brings us their side of this history-making case for marriage equality. With the help of the American Foundation for Equal Rights (AFER), their case was fought by Ted Olson and David Boles, two men who previously fought against each other in the Bush v. Gore Florida recount case.

By focusing on the notion of "separate but unequal," the attorneys battled it out against Proposition 8’s supporters through multiple trials and appeals. The case finally made it to the Supreme Court last spring where a 5-4 vote reversed the course of the proposition and legalized same-sex marriage again in California. The shockwaves of that ruling are being felt across the country, most recently here in Texas, where a federal judge ruled that the state’s ban on same-sex marriage is unconstitutional.

At one point, Ted Olsen says, "civil rights battles are won because you fight them." Thanks to Cotner and White, we get to see this defining moment in history unfold, culminating with the cameras capturing the couples celebrating their ability to legally get married.

Since the film strictly covers the plaintiffs in the case and the unlikely pairing of the lawyers who defended them, "The Case Against 8" is tailor-made for audiences who are already firm believers in the issue. It’s unlikely to sway (or even be viewed) by people who are against gay marriage or unsure of where they stand on the topic. That said, it’s an emotionally riveting story that caused more than a few tears in the audience last night.

"The Case Against 8" will screen again at 11 a.m. on Monday at the Rollins Theatre, at 11 a.m. on Tuesday at the Topfer Theatre and finally at 6:45 p.m. next Friday at the Stateside.