Celebrated filmmaker Jane Campion tackles the sunset days of the American cowboy era in “The Power of the Dog,” her screenplay based on a 1967 novel by Thomas Savage. Set in Montana in 1925, with the motor car just arriving on the scene, the movie centers on two brothers running a cattle farm. Benedict Cumberbatch is a mesmerizing, fearsome ball of fury as the macho one of the pair, while Jesse Plemons is also perfectly cast as the besuited gentler brother. When the quiet one falls for a widow (played pitch perfectly by Kirsten Dunst) running a restaurant, the furious one begins a war of intimidation, one rendered even more suspenseful and unpredictable by the entry of the widow’s gangly, effete son (Kodi Smit-McPhee almost steals Cumberbatch’s thunder in this role). The four of them swirl around each other with a growing sense of approaching calamity, underscored by unsettling music from Jonny Greenwood. As always with Campion’s films, the cinematography is exquisite, with metaphor and meaning in every frame. Campion is an “arty” filmmaker in the best and worst sense of the word: while the tension builds almost unbearably, the spare, unsentimental direction makes identification with the characters hard to attain. Nonetheless, The Power of the Dog is a powerful, intriguing movie, a must-see.