Doing justice to one cultural icon is a challenge. In Cadillac Records, writer-director Darnell Martin speeds through six, count ‘em, six music legends in two hours. It should come as no surprise that the result can be a bumpy ride. Mostly it plays like polished cable fare blessed with a run on the big screen, but there are a few highlights, including the most outstanding cast in recent memory.

A lauded veteran of biographical performances, Jeffrey Wright anchors the ensemble with his sly, paternal Muddy Waters (a man who, as history serves, unknowingly brought The Rolling Stones into existence through his amplified boasts and incendiary slide guitar). As Wright finds him, Muddy is stuck between singing about being a man and acting like one. When it’s often taken for granted that an artist actually comes from somewhere, seeing a persona such as Waters flourish in front of your eyes has a singular, exotic charge. It’s rare to witness it first hand, and just as rare in the movies.

As luck would have it Wright, who’s never entered a scene he couldn’t walk away with, could lose a little thunder to Columbus Short when the slack-jawed, thuggish charm of his work as Little Walter pins everyone to their seats. Much of the real Walter is unknown, so Short fills in the gaps with a proto-gangsta swagger that a more reverent performer would never have the balls to put on display. Walter pulls his gun as easy as he pulls out his harmonica and when he pulls the harp instead, you still might flinch.

It’s too bad the movie is so short on Short, or Wright, or Mos Def, etc. in its barreling clif-notes approach to the Chess Records legacy. The script is riddled with howlers and liberal dramatic license. Etta James’s early career is distilled to a few one-note vignettes of despair that trap Beyonce Knowles, delivering a surprisingly honed performance, in a perpetual cry for help. Adrien Brody is so detached as Leonard Chess he’s hardly worth mentioning except that Leonard’s brother Phil Chess is completely MIA here, a red flag for R&B connoisseurs. There’s precious little time for any of the characters to develop, and when it’s wasted on a young Rolling Stones “cameo” straight out of Walk Hard, it’s almost unforgivable.

Then the Chess catalog comes to the rescue. The recording sessions and onstage sequences are alive with sex and mythical energy. Even the characters who are less than impressive with spoken dialogue, such as Eamonn Walker’s Howlin’ Wolf by way of Batman, can seem larger than life. The songs are timeless, and when every last one of the leads are singing them as intended, with lust and sorrow and righteous anger you catch a glimpse of the Cadillac Records that might have been. A film with less of an agenda, and a lot more soul.

Cadillac Records hits theaters tomorrow.