Nah, I'll just solve the mysteries instead. But a hint would be handy: Is the discount only available if you use it while doing the mystery or is it still available once you're finished, ie between cases? PM me. :)
It's available anytime AFTER all three Scripted Mysteries in the Doomsayers triology have been completed. But, (and it's a BIG but), the prize will not take effect UNTIL you've gotten through all three. Sorry, no way around that. Once you have though, you can collect yer prize, so to speak, at anytime from Shady (in any of his usual haunts) anywhere in Sleuthville.
Might also be helpful to know that there are actually TWO prizes available. Down side is, you only get to choose one. And no, you can't go back again, redo the series all over, and expect to re-collect either the discount or the second prize. Nope, sorry, that one's been tried before (yeah, I know, that sucks, doesn't it?? ;-).
SO, when you do get through with it, make VERY sure that you choose your prize well, and when it's most needed.
Cause trust me, folks, you can't take the thing back and return it. Sorry.
*I can hear the E-mails and PMs to Fez Boy gripin' bout that one now....*
So, hope that clears up the befuddlement a little bit. Like Turtledove said, anything more than that is pretty much a spoiler. ;-)
So good luck, happy hunting, and give my best to the Shadowman!! ;-D