AUSTIN - In the two "Insidious" movies, Angus Sampson and Leigh Whannell play the two paranormal investigators who work with Lin Shaye, and I enjoyed how they almost felt like they were beamed in from another film with a more aggressive sense of absurdity. They had really fun chemistry together, and in the second film especially, they were a big part of what the films did well.

Last week, their new collaboration premiered as part of the SXSW Film Festival, and this time, the two of them are front and center. They co-wrote "The Mule," and they both play key roles in the film, with Sampson also serving as co-director with Tony Mahony. "The Mule" is dark and smart and deeply satisfying, a wicked little crime thriller with a grim sense of humor. Sampson's work in front of the camera is just as good as his work behind the camera, and I suspect "The Mule" is going to emerge as one of the films that audiences really love from this festival. It may be the most exciting surprise I've had since I got here.

Sampson stars as Ray, a guy who seems to be treated like a joke by everyone who knows him with the possible exception of his own mother Judy (Noni Hazlehurst). When his football team heads to Bangkok as a post-season celebration, Ray seems excited to be included. That's before his friend Gavin (Whannell) approaches him to explain the real purpose of the trip: they are going to buy a kilo of pure heroin and smuggle it back into Australia, and Ray is the one who is going to swallow and transport the 20 condoms full of the product.

Suffice it to say that things do not go well.

Hugo Weaving and Ewen Leslie co-star as Det. Croft and Det. Paris, federal agents who stop Ray at the airport. He follows the letter of the law and refuses to allow them to do a full digital search and also refuses to let them x-ray his stomach, which leads to them locking him down for a legal seven-day detainment at a motel. Ray is determined not to pass the drugs, and they're determined to watch him closely until he does, setting up one of the most deranged battles of will I've ever seen in a film.

John Noble plays Pat Shepherd, a local businessman who has a vested interest in the outcome of the situation, and he casts a big shadow over the rest of the film. It's amazing because Noble plays things at an absolute minimum, but he is crazy scary in the film. He strikes me as the kind of guy who is genuinely behind the scenes, calling the shots. He's not pretending to be Scarface. He's just a hard, cold thug with a shark's smile and dead eyes, and I love the way Noble plays the part. By contrast, Weaving's having a party from the moment he shows up. You can tell when an actor is taking pleasure in every little thing they get to do, and Det. Croft is such a happy asshole, so pleased to be busting Ray. His partner is far more irritated by it all, and Leslie allows his emotions to rule the way he behaves, a dangerous situation to be in for the detective.

There's a very tricky tone that the entire movie navigates carefully, sometimes funny, sometimes filthy, sometimes genuinely scary. Angus Sampson's performance has to be spot on in every moment, and he goes through a very honest evolution while spending much of the film flat on his back with stomach cramps. At the start of the film, Ray feels like a donkey. He's that guy who everyone laughs at quietly, the big thick kid who turned into the big thick man, and he really just wants to be accepted. When Pat throws an end-of-the-year party for the football team that Ray plays for, he announces that he's sending the whole team of vacation, and he also gives Ray a special award as player of the year. He gives an earnest speech about how Ray may not be the one who scores the most or who plays the most, but he's the one who embodies the spirit of giving it everything you've got. It's pure flattery, and Ray's parents are there to see it, his mother basking in the praise for him. That's all Ray wants, and when he finds himself cornered about the idea of smuggling in the drugs, it's that same longing for acceptance that drives him to say yes. He can't help himself. He wants to be one o the boys, and in particular, he wants Gavin to approve of him. Gavin seems to be everything that Ray aspires to, a guy who parties hard and lives loose and who does great with women. Sampson communicates all the longing that drives Ray, but he also does a great job of showing what happens when that curdles, when he starts to see clearly that the only one suffering is him. Ray may not be the brightest guy in the room, but he's the one with the most at stake here, and he's the one who has to get himself out of it. There's no one else really looking out for him. By the time the film's satisfying final moments play out, I felt like I'd seen Ray snap into focus and finally become a self-sufficient adult, and it's not overdone even one little bit.

As you might suspect from the set-up, there is some really gnarly stuff in the film, some grim moments that are going to be hard for some audiences. But a film like this is a gift to a distributor looking to cut a good trailer, because it's got plenty of familiar faces, and a ton of great moments and images to use. It's an easy film to explain, and it's such a stark conflict -- will he poop or won't he? -- that it seems like there's no way that's enough to drive a whole film. It is, though, and I really hope "The Mule" gets a shot at a real theatrical release in the US. While the film is very Australian, with several characters speaking in fairly dense accents, the film does such an outstanding job of just communicating intent in each beat that I don't think it matters at all.

"The Mule" is still seeking distribution. This confuses me.