"Right," John says, nods, and never would he have thought he would be attempting to create a new spell.

Or, well, it's more Sherlock who's doing the creating, but being there when it's in the workings - from the very beginning, even - isn't so bad either. Exciting, and... a bit of a reason to be nervous, because you never really know what can happen when experimenting with spells. But, hey, how would their society ever get anywhere if no one did that?

"So the spell is...?"