I was working with this idea when I was writing my own story but since I'm not following through on it, feel free to use it.
Treasure hunters who are dragged into the center of a war by one of their discovery. The war is centered around a race of being (demons if you must) from another dimension which consumes living matter. Much like humans, they attempt to farm those they consider food, coming through a portal connecting the two worlds. The human race had long been defending against these creatures with help from dragons, ancient creatures who despise the demons which came from another dimension. Dragons have a bond with some humans capable of magic, teaching those who have that power. But even with all that power, the demons could still not be wipe out due to the nature of the portal. The dragons understand the demons will consume everything in this world so a seal was made to block them since the loss of life defending against these creatures were too great. The seal was made over the portal but underestimating the demons' own magic, the dragons had to pour even their own life into forming the seal.
Years pass, the dragon mages are seeing signs of weakening of the seal as some mages driven by greed (power or otherwise) open small portals to the other world to borrow the demon's power. With more and more demons starting to come thur the tear in dimensions, a small war is beginning.
Two young mages setting off to explore the world and master their magic decides to become treasure hunters while they complete their magic training. They chance accross old dragon relics with the power to fix or destroy the seal.
As you can see the plot isn't finished. The world, magic and characters are all developed but since I am weak at writing up a plot, I don't have any idea how to continue. The general idea though is very extensive. So yea, if you like to take up this story, I'm happy to give you more information.