A rescue in Black Mountain #2

After some minutes, Thunderbard dropped two more symbols into the slot. The door creaked open. He followed the tunnel and came to the second door. Again, there was a slot in the door and a ledge in the wall. Different symbols made of baked clay were piled on the ledge. Thunderbard studied the symbols drawn on the second piece of paper.

He picked up the first nine triplets of symbols and dropped them in turn into the slot. But what was the tenth triplet of symbols that he had to drop? He started to think and to think.

After a while, Thunderbard dropped in three more symbols. The second door swung open with a jolt. There, waiting for him, was Thawmuch’s grateful son.