Today marks the return of a cult public television hit — Foyle's War. It previously appeared as part of PBS's big Sunday night Masterpiece lineup, but it won't be on TV tonight. For now, viewers will have to stream the show digitally. Acorn, the company that produces Foyle's War, has embarked on something of a Netflix strategy — raising the question of whether a niche pay portal can be a going concern.

Acorn has long sold videos and DVDs of the hundreds of hours of U.K. shows for which it holds North American rights. Now it's offering a digital streaming service that gives subscribers instant access to much of its extensive back catalog — and an advance look at programs it produces.

"We want consumers to think of Acorn TV as the primary destination for British mystery and drama television in North America," says Miguel Penella, the CEO of Acorn's corporate parent RLJ Entertainment. It's a brash claim for a market crowded by HBO, the BBC and PBS.

As Acorn expanded its ambitions, it bought a controlling stake in Agatha Christie's literary estate — and is now producing some of her mysteries for TV. The company is betting enough fans of British programs will add one more subscription to their virtual cart, along with Netflix or Amazon prime.

This season is to be the last for Foyle's War. Michael Kitchen plays Christopher Foyle, a senior police official turned intelligence operative at the close of World War II, and his performance has inspired a near-rhapsodic response from critics. But the financing for this season of the show appeared in doubt — so Acorn decided to buy the rights and produce Foyle's War itself, earning much of the cost back from foreign broadcasters

American viewers who want to see it right now will have to pay $5 a month or $50 a year. "For us, it is simply an opportunity to bring our content to consumers in a different, new way," says Penella. Acorn's decision to stream programs itself illustrates how the lines separating distributors, producers, syndicators and networks have blurred.

Good for Acorn, says Rebecca Eaton, the longtime executive producer of Masterpiece — but she argues that PBS has a public mission, while Acorn has a business plan. "To use public broadcasting, to use public television as a platform and a showcase for programs they might acquire," she says, "that's pretty good advertisement for selling them on down the line."

Millions of viewers watch Masterpiece every week for free, and Eaton says her program endures through changes in viewer appetites because of its sustained quality: "I think there's a tremendous interest in high-end British drama," she says. "And I think you can lay that at the feet of Downton Abbey, Sherlock, a lot of the programs we've had on the air — and why wouldn't a business want to spin that particular stuff into gold?"

Acorn says it currently has just 116,000 subscribers, but that's growing. And Penella says its revenues more than justify the cost of producing and streaming shows like Foyle's War: "In recent years, with the convergence of television and the Internet, we saw for us an opportunity to develop a proprietary digital platform that would allow our consumers, our audience to access our deep library — anytime, anywhere," he says.

Foyle's War will run later this year on individual PBS stations, but not on PBS as a network. And if anything, the relationship between PBS and Acorn evokes the frosty rapport between the two matriarchs of Downton Abbey: the Dowager Countess and Isobel Crawley. Collaborators, peers, competitors — in other words, frenemies.

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