Captain Clutterbuck's Treasure - S17.E5

When word comes around that there's a treasure buried in town, it's up to the trio to go and find it. To do so they need the help of the one man that has the *only* map, Lieutenant Commander Willoughby (Royal Navy, retired). It's up to Foggy to pay the 30 pounds the map's worth. The problem is... how many maps were sold in the first place? Foggy vows not to be near one cash dispenser again...