The adventure will begin with the players waking up in a room, with no memories* of who or where they are. The adventure will revolve around the players escaping and discovering who you are/were, as well as finding your place in the world.
While not wanting to spoil the fun, suffice it to say that the PC's are different from the norm. So the adventure will be as much about self discovery as well as the usual adventuring madness.
As I have a few surprises in mind regarding the players, I'll be doing a lot of the dice rolls myself, and revealing appropriate tidbits as the adventure progresses.
If the game goes well and the players are still interested I'd look at turning this into a regular ongoing campaign, so please design your characters with this long-term view in mind.
* The characters will have selective memory loss. While they will have no memories about themselves or the world they wake up in, they still retain the knowledge appropriate to their classes and skills. So a Wizard could still cast spells and be knowledgable about arcane theory, but wouldn't remember how he acquired this knowledge.