Corrupted Gem

(TBH THIS WAS WRITTEN BEFORE SEASON 2! MY PERIDOT AND THE CANNON PERIDOT ARE NOT THE SAME!) Every mission is the same, there's a monster, the gem's fight, pearl tries to send Steven home, bla bla bla. But what happens when a real threat to Gem kind is the monster they are facing? And what happens when that monster gets a hold of Steven before Pearl can send him home?