The next episode of "Grimm" season 5 will be its 98th story to air. Viewers are excited to know what mystery lies behind the keys when it reaches the 100th episode milestone.

This was the promise creator and executive producer Jim Kouf said in the first Comic Con he attended. The secret behind the seven keys, which figured periodically throughout "Grimm's" five seasons will be revealed on its 100th episode.

Kouf told Blastr they were surprised when the show was about to reach its milestone since many series don't get to last that long anymore. He said that when the episodes reached the 90s count, he thought "uh-oh, we'd better figure out what those keys are," adding "we always had an idea, but now we had to actually do it."

Episode 10 is bound to be more than just a peek to this mystery with its title "Map of the Seven Knights." The synopsis as shared by Spoiler TV says "Monroe gets a call from a relative in Germany that will bring Nick closer to his ancestors. Things get complicated when the nefarious group Black Claw is also after the same artifacts. Elsewhere, Capt. Renard helps a mayoral candidate get an edge on his opponent. Meanwhile, Trubel confronts Eve about Nick and Adalind."

Only two of the keys are with Nick so far. One was given to him by his Aunt Marie and the other from another Grimm, Rolek Porter. Four are in the Royal family's possession. These keys each belonged to seven knights believed to be Grimm ancestors. Could the call from Monroe's relative be about the whereabouts of the seventh key? One released photo for the forthcoming episode shows Nick and Trubel examining a key. 

It is believed that when these keys are put together, it becomes the map that leads to a powerful artifact that the royals claim would enable them to rule the world.