It had been 4 years since The Partridge Family ended, and David Cassidy had pretty much faded from the spotlight. He smartly passed on an animated version of Partridge that had bombed, and watched brother Shaun begin his rise to stardom on The Hardy Boys-Nancy Drew Mysteries. Someone convinced him that he could play a detective, too, so David landed a role on NBC's long-running anthology series, Police Story, which, like Partridge, was from Columbia Pictures Television (Now Sony Pictures Television). The end result was that Cassidy was spun off into his own series. Problem was, NBC could not find the right night for him.
David Cassidy--Man Undercover debuted as a mid-season replacement in November 1978, airing on Thursdays, but lasted just 10 episodes before NBC, then struggling to find a hit, pulled the plug. Cassidy reprised his Police Story role of undercover detective Dan Shay, but, sorry to say, even with a new hairstyle, he still looked too much like his earlier character of Keith Partridge. That, friends, may be what kept folks from tuning in. TV vet Simon Oakland (ex-Kolchak: The Night Stalker, Black Sheep Squadron) was his boss.
Here's a sample clip, including the open with a pretty bad theme song.
Never saw the show, so I can't fairly rate it.