This spell created an invisible force around a recipient that shielded them from magic missiles. Any magic missile striking the shield was directed back at whoever cast it, striking with full force unless the caster had other protection against magic missiles.
Once cast on a recipient, the caster could move the shield to another by willing it and uttering a single word and touching the new recipient. Additionally, assuming they knew the word of incantation, anyone else in the area could move the spell by using the same method. There was no limit on how many times the spell could be moved during its duration.