Let's say you need a crime solved in the 1940s. Simple enough, you say, just get yourself a hard-drinking, hard-smoking fellow in a fedora. Sure, he stands around staring at nothing while his inner monologue makes snappy comebacks. But he'll figure things out for you soon enough.
On the other hand, if it's suddenly the 1990s, well then you're gonna need a couple of underpaid, well worn cops, preferably one good-looking and the other good at making punny, less than considerate comments.
70s? You want a dude with some virulent facial hair who drives an awesome car or lives on a boat or has a partner who's a monkey or somesuch nonsense.
And if it's the 80s, and your life depends on someone solving a mystery of some sort, then by G-d you'd better get a male/female detective pair with serious shoulder pads and the kind of pent up sexual chemistry usually reserved for 16-year-olds at Catholic summer camp.
People like the characters played by the half-Jewish (and born again Christian) Stephanie Zimbalist and the not Jewish (duh!) Pierce Brosnan on the hit show Remington Steele. Because no matter how much they'd bicker and snipe, at the end of the hour, your case would be solved, guaranteed.
Of course for all that skill, they still wouldn't be able to figure out they loved each other. But that wouldn't be your problem now, would it?