A copper coin can destroy the empire's border defenses.
When accounting officer Su Yan was counting copper coins in the Tea and Horse Department, he discovered the Xining Chongbao with Xixia cipher text engraved on the edge - this was not an ordinary currency wear and tear, but a moth mark on Xixia's fine work to convey military information.
Behind the peaceful tea-horse trade, a conspiracy to erode the border defense of the Song Dynasty through copper coins has been quietly operating for two years.
When the numbers on the account books become the code to decipher the enemy's movements, the warehouses and forecourts become battlefields without smoke.
From abacus beads to beacon towers, see how a civil servant shook up the huge spy network across the Song and Xia Dynasties with a line of numbers and a copper coin, and guarded a thousand-mile territory amidst the sound of abacus beads.
The espionage war in the cracks of history, the cracks in the national destiny can be seen in the money hole.
