As long as you're listening to John Dempsey and Dana P. Rowe's score, you just might get a fix from "The Fix." On the evidence of one musical, this little-known American team (their off-Broadway credits seem to begin and end with ''Zombie Prom'') are capable of evoking Frank Loesser one minute, Jimi Hendrix and Pete Townshend the next, while freshly minting a hybrid musical form that embraces rock and rhythm and blues, hot gospel and Kander and Ebb. As to the show presently showcasing their music, that is, as Patti LuPone says nightly in ''Master Class,'' ''another story.'' For the moment, one is pleased to welcome undeniable talent even as one questions the uses to which that talent has been put. Dempsey and Rowe certainly couldn't ask for more heavy-hitting supporters than director Sam Mendes, here staging an original musical for the first time, and Sir Cameron Mackintosh, a long-standing Donmar ally (he put money toward both ''Assassins'' and ''Cabaret'') who brought the material to Mendes and holds the option on any future life for the show. It's difficult to imagine, however, what those prospects might be for an insistently sardonic, downbeat project that probably has about as much commercial viability as ''Assassins,'' with which it shares certain themes and a comparably wayward tone.
The story of a scheming political family who might as well be named Kennedy (leading man John Barrowman even boasts Kennedy-esque good looks), ”The Fix” begins as a pop opera ”Manchurian Candidate” of deliberately cartoonish characterizations. Ascending quickly up the political ladder, a philandering senator named Reed Chandler (David Firth) dies suddenly after one dalliance too many. His ambitious wife, Violet (Kathryn Evans from ”Mack and Mabel,” now sporting a Jackie O coiffure), and lame, polio-stricken brother Grahame (Philip Quast) instead pin their presidential hopes on Barrowman’s layabout son Cal. Before you can say spin doctor — indeed, Violet eventually gets a solo number titled ”Spin” — Cal is sent to army boot camp, married off to an available blonde (explains Grahame: ”blondes test better with the public”), and coached on attire, speech, and issues, of which only three matter: economy, crime, taxes. Grahame, in the meantime, expands his definition of ”family”: The Chandlers, we learn, are in thrall to the Mob.
In the second act, librettist Dempsey ups the stakes, and the show begins to stumble. Despite a brisk act opener for brothers Reed and Grahame, the tone turns solemn and bombastic as the creators succumb to a case of ”Les Miz”-itis.
None too mentally swift to begin with, Cal has fallen in with an ex-stripper (Krysten Cummings) who keeps him high on heroin, with the result that he is soon neglecting his political tutelage in favor of narcotics. With Grahame by now established as the resident Richard III (the crutches recall Antony Sher’s celebrated portrayal of the role), the scene is set for a (quasi-)repetition of events, with the anointing of yet another Chandler politico as the lights dim.
The intention, presumably, is a blackly comic expose of a fundamentally American malaise (Marilyn Monroe is explicitly evoked at the 11th hour to broaden the frame of reference), though ”The Fix” is better when it brushes satirically against such targets rather than trying to make a portentous statement. And admirable though the score is, it could profitably be pruned: One is aware late on of a series of putative showstoppers (among them a country-and-western ditty raising questions about Cal’s paternity) struggling to hit their marks; the combined level of volume and harangue proves wearing.
From the initial chorus in suits and sunglasses, resembling the male lineup in ”Smokey Joe’s Cafe,” Mendes directs with a smart hand that can’t forestall the ponderousness of the tale. With choreographer Charles Augins injecting a blast or two of clap-happy hot gospel to keep the company on the move, Rob Howell’s mini-turntable set and the excellent Howard Harrison’s fierce yet shadowy lighting create a sleek, soulless world amid which the Chandlers maneuver like the clawing voluptuaries of ambition that they are. Though Barrowman (the best Joe ”Sunset Boulevard” ever had) is as appealing as his part allows, the plum assignments go to Evans and Quast as two ruthless operators for whom bitchery turns deadly. It’s typical of the arc of ”The Fix” that Cal’s hymn to the future turns out to be grimly ironic, though on the evidence of the music expressing that vision, Rowe and Dempsey’s prospects look considerably brighter.