When a disabled surgeon is appointed by the Queen's Secret Court to investigate murders in the ghettos of Future London, he must destroy an alien threat within the Aristocracy.

"In the ghettos of a future London, a disabled surgeon must save the Queen's Secret Court from an alien threat within the Aristocracy."

Now, that looks good to me (then, so did the other one), but I'm not sure if I'm detracting from it overall by taking out the "investigating" part.

Also, I feel like I'm being a tad disingenuous by using the word "alien", since I'm sure people will be thinking "UFO's", but I'm referring to "something not seen before". I could use "mysterious" or "unknown" instead, but those words don't really GRAB you.

This sounds really good fun and something completely different. The genre is intriguing as seems like a mash up and something very unique to watch. Kudos on the idea. All I would say is the line maybe needs a little rearranging and I agree with TOAST that you should start with the setting as it bogs down the middle of the line and becomes slightly word heavy. Think all the details are there just needs a little reshuffling.

PS, I see you've taken previous feedback and improved your work. Well done. That's half the battle.