If Robert De Niro looks bemused during "Showtime", it's probably because he's suffering from déjà vu. In last year's "Fifteen Minutes" he played an NYPD detective with a lucrative sideline in tabloid television. Now he's back as an LAPD detective forced to appear in a 24-hour reality TV cop show with rookie patrolman Eddie Murphy. No wonder he acts like he's on autopilot.

Indeed, Tom Dey's disappointing follow-up to "Shanghai Noon" is little more than action comedy by numbers. The idea of casting method man De Niro opposite wild card Eddie Murphy must have looked great on paper. But all it really achieves is to make us hanker for earlier, superior capers like "Midnight Run" and "48 Hrs".

It's not the concept that's at fault but the execution. Twinning De Niro's grizzled veteran with Eddie's fame-seeking upstart is a neat gambit, and having William Shatner (playing himself!) give them a crash course in TJ Hooker posturing is a masterstroke. The problems start once it becomes evident the script has nothing for them to do except participate in an increasingly wearisome succession of shoot-outs, punch-ups, and car chases.

There are compensations. Rene Russo more than holds her own as a tough-as-nails TV producer, despite being saddled with the ludicrous name of Chase Renzi, and Dey has fun mocking every bickering cop duo from Starsky & Hutch to Riggs and Murtaugh in "Lethal Weapon". But there's surely something wrong with a comedy where the only belly laughs come from the selection of outtakes tacked onto the end credits.