masonary Key

I am in 2nd kingdom and I saw the message to return to find the mansonary key. I returned with the pie and saw message to look around the river. But I can not find any key to open the gate. please help

Did you return to Kingdom One with the pie? You need to drop the pie at the king's feet. You will then be able to find the key at a spot you weren't able to get to before. Look at the map for Kingdom One in the walkthrough and look for the purple diamond. You will need to approach it from the north.