Detective Conan is awesome.
I guess I was one of the few people here who collects the manga instead of watching the anime. I've been collecting them for two years now.
Tsunulia pretty much answered your question and you probably know it all by now, but I'll say it anyway.
Shinichi and Ran went to this theme park. Someone got beheaded in a murder. As usual, Shinichi solved the murder. The two men in black were one of the many witnesses. They were in a hurry. Shinichi suspected them after the murder was solved and followed them. The men in black was doing a trade. One of them was missing and snuck up behind Shinichi, knocking him out. They gave him this drug that was supposed to kill people, but instead, it turned Shinichi into a boy, Conan Edogawa.
Naturally, he ran to Agasha's home (his father's old scientist friend), fainted in front of the gate, Agasha found him and Conan explained everything.
He lied to Ran to live with her and her father (some drunk, hilarious, dumbass detective) cos of the fact that her father was a detective and the new cases will come in, hoping that one of those cases is related to the men in black, so that Conan (Shinichi) could get the antidote.
Along the way, he joined this school, befriended the rich/shy boy, the hyper/cheerful girl and the fat bully, and formed a group called The Detective Boys (I think).
Agasha gave Conan a voice-changing bow, a sleeping-gun watch, a pair of superstrength-kicking shoes and a pair of high-tech glasses (tiny locators also come with it).
It's filled with laugh-out-loud funny moments, drama, thriller and action. Also, the death scenes and the culprits did scare me before. I jumped out of my seat a few times. (Lex <--- scaredy cat)
. The music sucks, but everything else, including the sometimes cheesy dialogue are fantastic.
: Like that really wanna makes me want to spend that much of my money 
