Ok, towards the end, when the shingami Shidow (fishhead guy) came looking for the Death Note that Ryuk took from him, he eventually got it. So now I'm thinking that there is only one DN in the humans possession (not counting Ryuk's personal note). But that wasn't the case, as Light's original was still locked up at police HQ and Misa's was being used by the lawyer guy after Misa relinquished ownership again. Did I miss something? When did the third DN come into play?