Hardest Cases for Conan/Shinichi?

[Citan]

I think without a doubt the "Hardest" case for Conan to solve was "The Secret of the High Sales"

This is the only case I can remember where the DBs actually beat Conan without help. However that's only because the solution is so rediculously obvious that Conan, who is used to dealing with criminal geniuses, couldn't bring himself to accept it because there were so many holes and inconsistancies.

Spoiler:

The criminal was a jewel thief who hid his jewels in a building under construction that later became a crappy restaurant. He then became an employee of the restaurant, and repeatedly comes with excuses to get rid of the owners for short periods of time so he could search for the jewels. The DBs quickly and correctly realize that the whole set-up is just like "The Adventure of the Red-Headed League" from Sherlock Holmes, but Conan can't bring himself to accept anyone would be stupid enough to actually use such an obvious and rediculous plan. (He's too used to the meticulously planned out tricks of the criminal geniuses he's always battling.) It turns out the Criminal is just REALLY stupid, and when the DBs catch him and Conan realizes they were right the whole time he actually breaks down and starts berating the criminal for his stupid plan.