Board Thread:Episode Discussion/@comment-3125844-20150731045049/@comment-24397663-20150802105638

They saved Diana from getting to close to the royals, so using her when she is still so young for espionage on the keys is... very unlikely. Maybe when she's grown up (perhaps at the end of the season going by her grow-rate XDD )

Renard told Nick, that the royals have 4 keys, but it's not neccessarily only one family, that got all of them. We were told about 7 houses, so... the keys could be anywhere in europe.

One key 'went into hiding', but since the Hundjäger were after the Porters, I guess that wasn't the lost one.

So, Nick has two, one is missing, four are with the royals.

Given that, I would say Nick/Trubel are searching for the lost one.