MI-5, on BBC One (UK)
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streaming sites: BritBox

Originally aired in Britain under the name "Spooks." I haven't seen as much of it as I'd like, and even when I did watch it, I didn't completely follow everything that was going on (perhaps because I don't manage to catch everything that's being said). And I'm afraid I can never really remember any of the characters that well. But still, it's a pretty good show. It's about MI5 (the British Security Service), of course. They... like, counter terrorism, and stuff. Dunno what else to tell you, but it's definitely pretty dramatic. Much more deserves to be said about it than I can think to say, I'm afraid.