Poirot, on ITV (UK) / A&E & PBS (USA)
Acorn; Agatha Christie Wiki; IMDb; ITV Studios; PBS; TV Tango; TV Tropes; Wikipedia
streaming sites: Acorn TV; BritBox

This aired in the U.K. from 1989-2013. I'm not entirely sure when exactly it aired in the U.S., but I know it has aired on both PBS and A&E, at different times. So it's not purely a "Mystery!" series, but I think it aired there before A&E. Anyway, I haven't watched nearly enough of this, but I've always liked it whenever I did. It's a good show (actually a series of TV movies), based on Agatha Christie's Poirot novels (which I'm afraid I've never read). David Suchet plays Belgian detective Hercule Poirot to perfection. And there's this guy named Hastings who sort of works with Poirot when he's solving murders, though he's not much of a detective, himself. There's also Chief Inspector Japp of Scotland Yard, who often is investigating the same cases as Poirot. And Poirot has a secretary named Miss Lemon. And I really like the theme music, "The Belgian Detective," by Christopher Gunning. I wish I could think of more to say about the series. I really need to watch some more of it someday....