The mystery deepens

On the 24th Granddad received another mysterious package. Yes, there was even more chocolate and another strange message:

You remember that the "key" to the cypher was in the last box.
Go on, you solve it.
The rest of the family was just too busy to help poor Granddad. He puzzled over it for a while. Then he decided to wait until he had some detective help.

On Christmas eve our house was full of friends. Everyone puzzled over Granddad's latest mysterious message. What does it mean, H = 12? N = 18?

It took a smart 6th grader to help Granddad solve the cypher. The message?
Aha!
The whole party trooped out to the garage.
(Where they promptly discovered that I'd cleaned up the breezeway by shoving everything in the garage...oops)

In the trunk Granddad and his helpers found...another little box!
The key from the last box fit this box.

Eagerly they opened it up...

inside was another key!

The mystery is NOT solved....

but he's getting close.