Merthur AU (angel!Merlin/human!Arthur). When Merlin sees Arthur for the 1st time, all he knows is that he wants to protect him. When Arthur's in danger, Merlin accidentally ends up on Earth while trying to help him. Now he must stay in Camelot and befriend Arthur until angels find him to bring him home. Their growing love is forbidden though. What can Merlin do now? Leave or die?