The movie is careful not to push too far into Freudian psychodrama. Brian’s mental collapse is not directly attributed to his abusive father or to the pressures of fame. At a certain point, the sounds in his head take on a sinister cast, and his odd behavior and paranoid ramblings frighten his bandmates and his first wife, Marilyn (Erin Darke). LSD doesn’t help. By the time he meets Melinda, though, his breakdown is in the past. He strikes her as a sweet, soft-spoken eccentric, a pampered rich guy who is also kind and vulnerable. He shocks her sometimes by referring almost casually to the trauma and abuse in his past and gradually reveals the terror that governs his present-day life.

If the ’60s half of “Love & Mercy” is, in part, a trippy excursion into a golden piece of the California past, the ’80s section is a spooky Los Angeles noir. Told almost entirely from Melinda’s perspective, it follows her discovery of the hidden, sinister dimensions of Dr. Landy’s apparent benevolence. A jolly, friendly fellow on the surface, Landy is both a one-of-a-kind creep (Mr. Giamatti’s smile will give you nightmares, as will his hair) and a recognizable type of villain. Melinda, whose sunny disposition masks a steely, icy resolve, makes a very satisfying foil, and Ms. Banks’s astute performance, in a series of eye-catching period-appropriate outfits, is what binds the film together. Melinda is the only person who can love and appreciate Brian for who he is, and as such she is the stand-in for the rest of us, who admire what he accomplished.

This film deepens that appreciation and illuminates its sources. Mr. Pohlad’s deft narrative sense and careful visual style are complemented by the work of Atticus Ross, whose sonic collages —“score” doesn’t quite do justice to his achievement — take us deeper inside a musical mind than we might have thought possible. “Love & Mercy” doesn’t claim to solve the mystery of Brian Wilson, but it succeeds beyond all expectation in making you hear where he was coming from.