An explosion rocks Sam's world, causing her to lose her memories, and she finds herself lost in a forest with a stranger. There, she and the stranger meet an older man named Albin, who provides them with only enough information for them to begin a mission he is suddenly sending them on. Through a magical portal he creates, they are transported to another world to search for a mystical key. Completely lost and confused, they find shelter in a cave behind a waterfall, only to discover that it is not vacant.

Chris, the owner of the shelter, is sent on the same mission, except he has been there for two years with no way back home. The three of them band together to continue the mission, recruiting others along the way. A ruthless king from another world who wants the Key and its powerful counterparts for himself sees Sam as a possible heir to his throne. In an effort to thwart their mission, he throws many trials her way to test her strength and abilities, making their mission harder than it was before.