"That's why it's proving so hard to find. There's no point in going for Tom, if he can be resurrected every time using the last Horcrux, and he daren't make any more. But he knows that I know his weakness ... and he must have taken out a contingency plan in case I did find a way to return, or in case I'd passed on the secret of how to bring him down to someone else. The item in this box is his solution to that problem."