He knew the spell the instant he felt the power draining from him; it was a favorite of his enemies, of the kind of magic they practiced. He should have been prepared, seen it coming. He would be defenseless for a time: hours, perhaps even days if the caster was strong enough.
They wouldn’t give him a chance to recover, of course. Somewhere, somewhere close, there was a swordsman or a knife-wielding assassin preparing to deliver a coup de grace his sorcerer master was too afraid to execute himself.
But whoever he was, he was in for a toothsome surprise.