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They’re both called Brian Wilson, but in the bittersweet biopic “Love & Mercy,” Paul Dano and John Cusack are essentially playing two different people.

The Brian Wilson of the mid-’60s was the producer and principal songwriter of the Beach Boys. With a little help from his friends, he transformed the sandcastle of surf music into a cathedral where acolytes like the Beatles worshiped.

The Brian Wilson of the ’80s was a fallen angel with broken wings. With a lot of hooey from his fiendish shrink, he buried his head in the sand until a lovely lifeguard came to the rescue.

The young Brian (Dano) is from a musical family in suburban LA. His particular obsession is vocal harmony, which he learned by listening to Four Freshmen records. Prodded by domineering father/manager Murray (Bill Camp), the three Wilson brothers, along with cousin Mike Love and friend Al Jardine, turn California culture into a global brand. (The opening-credits montage, like everything else in the film, is uncannily accurate about the artifacts of the era.)

In 1965, Brian stops touring with the band to concentrate on songwriting and studio techniques that might rival those of his hero Phil Spector. When a friend gives Brian some LSD, it unleashes a tidal wave of creativity. Its purest expression is the album “Pet Sounds,” which adds sound effects and spiritual yearning to the pop palette. But the album doesn’t sell well, and Love joins the jealous Murray in belittling Brian.

Yet as we see in the documentary-style studio scenes with the hired musicians called the Wrecking Crew, Brian is jousting with the windmills in his own mind, and in the meticulous recording of “Good Vibrations,” he wins. Yet it’s essentially his last stand, as the sessions for the unfinished “Smile” album drive him mad.

In the parallel narrative set 20 years later, Cusack plays the middle-aged Brian, who is virtually held prisoner by his live-in psychiatrist, Dr. Eugene Landy (Paul Giamatti). Landy has helped Brian kick drugs and lose 100 pounds, but he has also separated the patient from his friends and made himself the beneficiary of Brian’s will.

On an outing to buy a new car, Brian escapes his ever-present bodyguards by motioning for saleswoman Melinda (Elizabeth Banks) to join him in a showroom Cadillac. Thus begins a furtive love affair, legal action against Landy and Brian’s ultimate resurrection.

“Love & Mercy” is artfully but unobtrusively directed by Bill Pohlad. A film producer known for Oscar-winning films such as “Brokeback Mountain” and “12 Years a Slave,” Pohlad has surrounded himself with award-worthy talent on both sides of the camera, from music supervisor Atticus Ross to the art department to the stellar cast.

Dano and Cusack are a study in contrasts, as the young Brian is a bruised Buddha with a beatific smile and the old Brian is a brain-damaged man-child tapping SOS on his piano. Where he’d be without Melinda’s love and mercy, God only knows.

What “Love & Mercy” • 3½ stars out of four • Run time 2:00 • Rating PG-13 • Content Thematic elements, drug content and language

Joe Williams is the film critic for the St. Louis Post-Dispatch.