If you have a rotom go to the galactic building in Eterna City. Enter it and make a left. Until you hit the wall, go north. go between the machine and the wall left of you and press A on the wall north of you. it will say would you like to use the secret key and say yes. a door will show up and go inside. make sure to bring a rotom so you can change it's type and form. For example, washing machine rotom, microwave rotom, refrigerator rotom, mower rotom, and fan rotom.
P.S. if you look at rotom's name backwards it spells out motor!
Pokemon event
In Pokemon Platinum you dont get the key from a grunt you get from the detective, before getting the key you have to go talk to prof. rowan in the library .
go on Pokemon Platinum Walkthrough you'll might get the idea.
You can only get the secret key in Pokemon Platinum
its easy but hard
you need wifi do get it!
It's exclusive to Pokemon platinum version.
check serebii.net for info on upcoming events for Pokemon Diamond,Pearl,Platinum.
platinum is coming to America in 2009 ask someone in japan
Looker will meet you at the warehouse and he will have the key.
Go to www.pokemonplatinum.com and click mystery key
i think the key is "ENTER"