Much was lost in transition from BBC miniseries to American movie in "The Singing Detective" -- wit, soul and texture have been replaced by shallow obviousness and glib sentiment. The film is sour, unpleasant and, given its stylistic flourishes, curiously inert.

Robert Downey Jr. lets the tears flow and the venom spew as Dan Dark, a mystery writer laid up in a hospital bed with a case of psoriasis that has consumed every square inch of his skin, coupled with arthritis that leaves him hardly able to move. Dan's condition also makes him prone to hallucinations, and he takes solace in them, imagining himself as the protagonist of one of his novels. (None of this has changed from the miniseries, but the hero there, played by Michael Gambon, had a far more resonant name: Philip Marlow.)

In his mind, he's the singing detective, a 1950s pop crooner (and not a particularly good one) who solves mysteries on the side. And in the story he imagines, Dan has been hired by an unsavory acquaintance (Jeremy Northam) to solve the murder of a prostitute.

It soon becomes clear that the only thing driving Dan's third-rate narrative is his ingrained misogyny. All the women in the story are versions of either his wife (Robin Wright Penn), who, although she's apologetic about it and it's hard to blame her, has been unfaithful to him; or his mother (Carla Gugino), whom he blames for his wayward life. In flashbacks, we see that the young Dan caught his mom cheating on his dad with a handyman (again played by Northam).

Dan's illness and his failed relationships have left him a bitter shell of a man, and Downey, never a shy actor, channels rage, paranoia, petulance and vulnerability with quicksilver intuition. Yet he's so talented that he makes all that look easy. What's difficult is making Dan an intriguing person, and Downey never quite accomplishes that. It's a proficient performance, but never a moving one.

But it's not his fault that "The Singing Detective" is as dull as it is. The opportunity to glide in and out of fantasy and reality ought to be as liberating for director Keith Gordon as it was for Jon Amiel in the miniseries -- particularly given that Gordon's last feature was the terrific, underrated romance "Waking the Dead," in which the protagonist was similarly afflicted by flashbacks and visions.

The back-and-forth here feels labored: There's no anticipation to return to the hospital when we're inside Dan's mind, or vice versa. Gordon stages the detective scenes with a minimalist artificiality that only emphasizes how flat and underwritten they are, and the hospital never buzzes with any authenticity -- which the miniseries had in abundance.

Even the lighter elements, like Dan's relationship with his comely nurse (Katie Holmes) and the two hoods (Adrien Brody and Jon Polito) who wander around like Rosencrantz and Guildenstern, wondering what their purpose is in the story, don't amount to much.

The worst scenes are between Dan and his psychiatrist, played by Mel Gibson (who also produced) in a mugging performance. Appearing bald and bespectacled so as not to upstage his friend Downey, Gibson plays Dr. Gibbon as a borderline-incompetent loon, despite a script that calls for the shrink to be surprisingly effective at exorcising Dan's demons.

Dennis Potter, who wrote the revered miniseries and is the sole credited writer on the movie, died in 1994, so he wasn't able to shepherd this project to completion. Who knows what he would have thought of how Gordon and Downey have handled his material, but with the miniseries available on DVD, there's little reason not to go directly to the source and avoid this unfortunate crib-sheet version.

"The Singing Detective," a Paramount Classics release, runs 109 minutes. One and a half stars out of four.