He wrote the iconic "Fun Fun Fun," but apparently Beach Boy Brian Wilson wasn't having much of his own during the group's heyday in the '60s.

"Love and Mercy," the new biopic about the legendary songwriter, reveals the tortured soul behind the tunes that defined a generation. Thanks to stunning performances, it's a must-see – especially for boomers, who grew up on the songs of the Beach Boys.

In an inspired feat of storytelling, director Bill Pohlad alternates between two narratives: that of a young Wilson (Paul Dano), circa 1965-68, and of a post-Beach Boys Wilson (John Cusack), twenty years later. Although this technique is a bit disconcerting at first, it ultimately – and surprisingly – works. Both Dano and Cusack are excellent. Soft-spoken and vulnerable, each portrays a man haunted by a need to make music yet often beaten down by those closest to him.

It's riveting to watch Wilson set out to make "the greatest album ever," especially knowing that "Pet Sounds" really did turn out to be recognized as one of the best. The scenes in the studio are fascinating, with Wilson bringing in dogs to bark on the record, testing out musical sequences that shock and impress the musicians themselves, and producing sounds that were simply never heard before. His genius is obvious – "You're touched, kid," a musician tells him, admiringly – but so is his madness.

Wilson has a panic attack on a plane and admits he hears voices in his head. Eventually, he's diagnosed as a paranoid schizophrenic and, for three years, he doesn't leave his bed. His legal guardian, therapist Gene Landry (Paul Giamatti), keeps him so overmedicated, he can barely function.

By the time Wilson meets Cadillac dealer Melinda Ledbetter (Elizabeth Banks, in a quietly brilliant performance), he is in dire need of a savior. She bravely and compassionately rises to the challenge. God only knows what he'd be without her.

I don't know about you but I had no idea of the pain Wilson was suffering while the world was bopping along to his infectious songs. Not only was he trapped under the control of Landry, who betrayed his trust to a criminal degree, but he was beaten so badly by his father that he lost 96 percent of the hearing in his right ear.

Dano and Cusack internalize this pain so deeply and completely, they somehow both manage to become Wilson. This is especially amazing considering they look nothing like each other and Cusack has no resemblance to Wilson at all.

Together, though, the two actors create a disturbing and unforgettable portrait of the man who provided the soundtrack to so many of our summers.

"Five years from now, no one is going to remember you or the Beach Boys," his father says, cruelly – and incorrectly.

Knowing what he knows now, with the heroes and finally villains revealed, it's too bad Wilson can't go back in time to do it again.

Lois Alter Mark blogs at Midlife at the Oasis and is a regular contributor to Huffington Post. She is the reigning champion of Blogger Idol and was recently named Humor Writer of the Month by Erma Bombeck Writers Workshop. Lois won BlogHer Voices of the Year Awards in 2012 and 2013, and writes regularly on pop culture and travel. Because of her blog, Oprah Winfrey selected her as an Ultimate Viewer and took her to Australia on the trip of a lifetime. A member of the San Diego Film Critics Society, she was the Flicks for Kids editor at NickJr.com and a contributing writer for Entertainment Weekly for more than a decade. Transplanted New Yorkers, Lois and her husband of 32 years now live in San Diego, where they have turned into weather wimps and complain about the pizza. Their grown kids are, of course, both on the East Coast. You can follow Lois on Facebook or Twitter.