Possible Clues:

• Start game with cunning plan
• A plan to get what's precious in layers (9)
• The scheme of what's precious in layers?
• According to plan it's precious in layers
• The plan is to have the precious stone come in layers
• A plot of layers of stone
• Trick
• Plot the precious stone in layers?
• Are the layers just a little worthy, according to plan?
• Layers of rock with precious stone? That could be a trick