By Jeff Labrecque
Updated March 06, 2015 at 12:00 PM EST

Jay Duplass was disturbed—but fascinated—every time his friend, J. Davis, would go on one of his long, obsessive digressions about Charlie Manson and the Manson Family murders. “He always liked how upset it would make me when he would talk about this stuff,” Duplass says about his friend, an editor who cut his 2011 documentary Kevin. “But he just had this very personal, slightly disturbing, mysterious, and funny story that he just kept talking about, and one day, he sprung it on me that he wanted me to act in it—and this was before I had ever acted in anything.”

Duplass, who has appeared in Transparent and The Mindy Project when he’s not working behind the camera on HBO’s Togetherness, stars in Manson Family Vacation, Davis’ directorial debut that will premiere at SXSW on March 16. He plays a successful L.A. lawyer and family man whose life goes slightly helter-skelter when his slacker brother (Linas Phillips) comes to visit, intent on touring the infamous Manson Family murder sites. “We’re calling the movie a dark comedy, but like Mark’s and my films, it’s really a relationship movie—maybe a little darker than what we normally do, and a little stylized too,” says Duplass.

Manson has been in jail now for 45 years, following his conviction for planning the rampage of gruesome murders that included Sharon Tate in 1969. The 80-year-old still has followers and fans—he might even be newly married. So the brothers in the film meet plenty of squirrely characters during their macabre road trip across Manson Family history—some might even be threatening. Tobin Bell—Jigsaw himself—plays one of them named Blackbird. “I’m not going to lie, Blackbird is a scary dude,” says Duplass. “But he’s also very intelligent, very thoughtful. There’s a method to what he’s doing and it makes sense. There is so much more to Tobin than a quote-unquote bad guy, and that was super-important to us in terms of the role.”

Though Mark Duplass is one of the film’s executive producers, Davis’ film is the rare project where the two brothers, who’ve co-directed four features in addition to Togetherness, are not the primary collaborators. “The way that we talk about it is that it’s really healthy to have our little affairs on the side so that we can come back together and work together and feel good about it—feel like [working together] is not the only thing that we have.”

Togetherness, which stars Mark, Melanie Lynskey, and Amanda Peet, has become a critical hit at HBO, and the Duplass brothers, after years of scrimping by with micro-indie budgets, seem to have found they home. “Without a doubt, absolutely no question, the climate in television is open—everything is possible,” says Duplass, who starts shooting season 2 in a few weeks. “We came up with this idea that seemed so big and thought it could go on forever, so we’re really sort of doing long-form movies. It doesn’t feel like a compromise on any level. It feels like win-win-win all over the place. And for better or worse, the feature-film climate is not that way. People are scared. Distributors are scared. Studios are scared. They have to be very, very careful about what they make because it’s not easy for a movie to do well. So I don’t know… it feels like something’s got to give. It feels like a collapse.”

Below the striking new poster for Manson Family Vacation, watch Duplass, Phillips, and Davis talk about their film in the 2013 Kickstarter appeal that got their film off the ground.