Nick's Key

Nick's Key is a small green item that folds much like a multi-tool or butterfly knife to hide its purpose. Marie Kessler gave the key to Nick Burkhardt after she had been attacked by Hulda. Sean Renard seems very interested in obtaining it, having sent Adalind to extract it from Nick by placing Hank's life at stake. Many other people have attempted to obtain it for the Royal Families too, usually ending up being killed in confrontation with Nick. The key is later revealed to have a map of some sort carved on the outsides of the folding arms. Nick Prints the map.

Nick later matches the map on the key to an unknown map in an atlas.

The page from the atlas included the point where fifty-two degrees north latitude intersects the shoreline of continental Europe. It seems to be somewhere in France.

When Marnassier comes to Portland to receive the key, Kelly Burkhardt told Nick its origins. She reveals that the key is one of seven keys that belonged to seven knights who were ancestors to the Grimms. They worked for the seven families in the twelfth century. After sacking Constantinople in the Fourth Crusade, they took the treasure back, made a map on the seven keys, and each took a key. The keys, when put together, reveal the location of a treasure. Among it is an artifact so powerful that, if held by the seven royal families, it would allow them to rule the world.

A man called Sean Renard to warn him that the Royal family had sent a Nuckelavee to retrieve the key.. In the next episode, the Nuckelavee confronts Nick and is killed.

Renard takes the key from Nick's desk at the precinct and later returns it to him.

Nick later shows the key to Hank and explains a bit about its origins and why everyone is after it. He also reveals he's wearing it around his neck, so now anyone who wants it, will have to kill him to get it.

Trivia

 * The appearance of the key changed during the first season. When the key is first seen in the pilot episode, the etched image on both sides is that of, what looks to be, a creature. Later during the season, the etchings changed into a map.
 * Although not explicitly stated, it looks like the key is made from bronze, which has oxidized green due to the artifact's age.