Really not as clever as you think it will be. It's a Moffat, so like a Joss Whedon, you know it will make you like characters before destroying them. That kinda kills the twist, and makes it far more predictable than the creators think it will be.
Blah blah great cast. It's got Stanley Tucci in it. He's fantastic even when he's in dross (*cough* Bird Box *cough*). Actually, much like Bird Box, this felt like something that was desperately trying to follow in the footsteps of other, greater shows/films.
Presumably this is supposed to be the start of a series of mysteries solved by Jefferson Grieff. If this installment is anything to go by, I won't be bothering with the others.