The Mane Six all bring their 'key' gifts to the traders' exchange to see if they can get some handle on what they might be worth. Some merchant (it would be nice if it wasn't a pony but was a Griffon or Minotaur although someone has suggested the shopkeeper from Magic Duel) offers them ludicrous amounts of money for them. He's recognised them for magical artefacts, something in which he/she is a black marketeer.
There follows a typical Key episode crisis/resolution with Twilight reading out bits of their journal entries. When they realise they've given away gifts of friendship, they feel incredibly guilty and all get the rainbow eyes effect. There follows a confrontation with the trader who initially refuses to give up his new acquisitions, even for a full refund. Twilight invokes the Magic of Friendship, stating that such a thing cannot be bought and sold and that these items belong with those to whom they were given. Much to everypony's shock, the journal transforms into a key with her cutie mark on the handle emblem. Magic flashes out from the Key of Friendship to the other five artefacts and they all all transform into keys and fly back to their rightful owners (those whose cutie marks match the emblems on the key-handles). Chains appear around everypony's neck and the keys attach to them. Twilight sternly tells the merchant to take his money and go. Thinking himself lucky that the magic on the items hadn't done him harm, he does so.
Everypony is excited at finding the keys. However, there isn't time to open the Box yet (Twilight rightly insists that they do so in controlled conditions and with as many magical protections in place as possible). The Equestria Games are about to begin, so it's off to the Crystal Empire.