6/10
If it wasn't a finale case, maybe I'd bump it up, but it's so so bad as a finale that I can't help but hold that against it. The villain is just.... there. The surrounding cast is just...... there. When I ranked G1-3, I talked about how it showed you but didn't tell you something about a big twist and that I didn't think anything but 6-5 did that, but now that I think about it, the cat flap is another example. It's a cool twist, but it's definitely the high point of the case, but that's kinda embarrassing for a finale.
This is our main foray into Shady Gregson, though, which is the best Gregson, and is why I like his character so much. And the list of names you get right before the credits is a hell of a cliffhanger to leave you on. I am certainly glad we got G1 and G2 at the same time, or otherwise I would've been
pissed
.