Remus had never intended to stay where he had cast his spell from. He darted about ten steps closer to the door as his spell was traveling, and lucky he did so, as magical ropes just missed him. That had been too close. He was forced to remember now his 'famous last words' to James. How had a midnight foray into a library gone so utterly wrong?
Well, the spell had one him ten more steps towards the doorway, so he decided he could continue this, if it won him several steps at a time. Though how long before his adversary noticed his advance?
On that note, Remus had likewise noticed his adversary's movement. He still could make nothing out in the dark. Instantly, Remus had a brilliant idea. He sent a spark of fire flying at a bookcase about 9 meters from his position, darting backwards (ooh, away from the door, it pained him to do it but it pained him more to be predictable).