Hidden assets and secrets
As he started decrypting the letters, they revealed instructions about hidden assets and key family secrets.

‘Look here,’ he said, pointing out a phrase that mentioned a secret bank account. Another letter detailed the existence of a hidden property.
Each line he decoded was another revelation, and I could hardly keep up. ‘Your parents had hidden far more than just money,’ he concluded.
This was huge; I finally had something tangible to go on.