“Rudderless,” William Macy’s directorial debut, is uneven to say the least. It has a sincere heart, but it lacks the structure needed to be a truly powerful film. It often comes off as flat and messy. But the film has one saving grace: Billy Crudup’s immensely powerful performance.

Crudup plays Sam, whose life falls apart when his son Josh dies in a school shooting. After the tragic death, Sam resorts to alcohol for comfort, and he is so emotionally distraught that he is unable to hold a job. Soon, he finds himself living on a boat, unable to keep his luxurious house and too proud to ask for financial help from his ex-wife (Felicity Huffman).

Just when he hits rock bottom, Sam discovers a box filled with CDs of his son’s music recorded in the months before he died. Nearly overnight, his son’s quirky songs lift Sam’s spirits and he begins to learn them on guitar. When Sam decides to play one of the pieces at a local cabaret bar, he meets Quentin (Anton Yelchin), who shares a passion for similar music. As the two develop a friendship, Sam begins to see his son in Quentin.

As Sam, Crudup steals the picture with his raw performance that always remains grounded in truth. Even though the script is scattered with trite dialogue and awkward plot gaps, Crudup’s immensely powerful acting partially compensates for the errors.

But as talented as Crudup is, it does not distract from the film’s lack of dimensionality. The minimal editing and lack of artistic camerawork make it clear that “Rudderless” is very much an actor’s film. Interestingly, the missing stylization of the film renders the piece more realistic and creates a unique flow to the piece similar to one found in a staged play.

There are a few awkward casting decisions that detract from the power of the film’s drama. In an effort to draw younger audiences, pop star Selena Gomez plays Josh’s ex-girlfriend. The former Disney Channel actor is only on screen for a few minutes, disrupting the flow of honest acting with her hyperbolic lashing out at Sam. The talented Laurence Fishburne also has an uncharacteristically small role as the owner of the local music store. Both of these actors seem out of place in their throwaway roles.

Despite the problems the film has, it always comes back to Crudup, who guides “Rudderless” through its rough patches. “Rudderless” is far from a perfect artistic achievement, but Macy succeeds in taking the audience on a surprisingly elaborate psychological journey.

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A version of this article appeared in the Thursday, Oct. 16 print edition. Email Daniel Lieberson at [email protected].