I saw a client back in April, and everything was fine, a perfect gentleman, etc. The next day he sent an email asking for an overnight "date". He was less than thrilled with my £800 asking price.

He sent a few other friendly emails, then stopped emailing when he asked me to wear a certain outfit that I don't have and don't particularly want to buy (I told him if he provided it, I'd wear it). So, I figured that was the end of it.
Well, last night I noticed I had an email from him asking to see me again. Sure, no problem. It was late so I decided not to reply until today. So, I've gone to reply and I have two others from him, one moaning about my lack of reply (it's been less than 24 hours! sheesh!) and one other, which has kind of given me the heebie jeebies. Should I be concerned about this, or is it just a bit of harmless fantasy?
Here are some abstracts:
"... then blind fold you, lead you to the bedroom, you are in front of my mirror...,"
"....when my friend creeps in the room, kneels in front of you and starts..." (first mention of a "friend")
Nothing overtly menacing, just that. The rest of the email is just sex stuff. His previous emails have all been friendly chat or confirmation, this is new.
Not sure if I should reply with "sounds great, it'll be double my rate for your friend to join in" or "umm, don't think so, sorry." ?