Riding on the great theme music by Lalo Schifrin (whose most notable TV work would have to be 'Mission:Impossible'), the viewer is taken on a fast moving, one-hour journey shadowing (pun intended) a gun-toting, California detective, whose cases always get solved with fisticuffs, bullets, and a beautiful woman at his side (think: "Captain Kirk" meets "Thomas Magnum"!).
With a base cast of three people - - Mannix, his secretary, and a police inspector - - we were treated to a new guest star nearly every week. Whether they were good guys or bad, they always seemed to be cast right for the role they played! Even though the plots were basically the same from week-to-week, they somehow were presented with a new feel to them, that made us come back for more!
By today's standards, the "violent" aspect of "Mannix" would be considered tame, but, back in the 70's, the sight of car chases, fist fights (with Mannix always seeming to give as good as he got, but usually ending-up with a black eye in every episode), along with the occasional shoot-out was exciting, with very little blood being spilled (or, at least, not to the degree of today's unnecessarily gory scenes).
As seems to be common for most cop shows, Mannix was always arguing with the head police detective (who changed from time-to-time), with the trite "Stay-out-of-it" speech from the cop, and who might have been considered a "heavy", but, it was clear that they were on friendly terms.
Gail Fisher, one of the few black characters of the time cast in more than a cameo role (similar to Nichelle Nichols, "Lt. Uhura", of "Star Trek" fame), played Mannix's secretary, but she was viewed and treated as a person and Mannix's personal friend, as opposed to being just a hired telephone-answerer and bookkeeper. It would not be "politically incorrect" of me to say that white audiences accepted her as more than just a token black.
This was one of my favorite shows, back in the day!