Let's make a new TV rule right now: From here on out, no one is allowed to produce a Western unless Robert Duvall is somehow involved. Whether it's a starring role or just a bit part, the man needs to be on the screen and in the saddle. That's all there is to it.

The actor who wowed millions of television viewers with his captivating performance in the 1989 landmark miniseries "Lonesome Dove" brings his talents to the genre once again in AMC's marvelous four-hour old-West saga "Broken Trail." And it's a role that fits him like a comfortable, well-worn Stetson.

Duvall, 75, plays Print Ritter, a grizzled cowpoke who enlists his estranged nephew Tom Harte (Thomas Haden Church) to help him drive a herd of 500 horses from Oregon to Wyoming. But what looks to be a full-speed-ahead odyssey of male bonding quickly becomes riddled with complications.

While making their way over the verdant plains, Ritter, Harte and their traveling companion, Heck Gilpin (Scott Cooper), cross paths with five young Chinese women who have been sold into slavery and are being transported to a mining-camp brothel run by the formidable Big Rump Kate (Rusty Schwimmer).

At first, the men have no intention of intervening. They're all about minding their own business and meeting a deadline. But following a violent confrontation with the slave trafficker, they shift into good-Samaritan mode, rescuing the women and incorporating them into their caravan.

This act of decency turns out to have huge repercussions. An incensed Kate hires a sinister dirtbag by the name of Big Ears Bywaters (Chris Mulkey) to round up a posse and retrieve her missing goods. And throughout the harrowing drive, the suspense builds as Bywaters closes in on his would-be prey.

Deftly directed by Walter Hill ("The Long Riders"; the "Deadwood" pilot), "Broken Trail" is AMC's first original movie, and it's encouraging to see that so many things turned out so right on this maiden voyage. Give some of the credit to Duvall, who not only delivers an Emmy-worthy performance, but in his role as executive producer, reportedly fought off attempts by AMC bigwigs to inject more action and gunplay into what was designed to be a character-driven story.

As it is, bullets do fly on occasion in "Broken Trail" and Alan Geoffrion's masterful script doesn't shy away from the brutal realities of frontier life. But the overall tone is one of quiet intimacy as much attention is paid to the nuances of personal emotions and expression. At its heart, "Broken Trail" is a simple, lovely story about wayward souls struggling to find comfort and civility in the company of fellow human beings.