In 1857 the Tweed Fisheries Act made it illegal to fish for salmon in fifty square miles of open sea off the mouth of the River Tweed. This ban, enforced by the Tweed Commissioners, infuriated the local fishermen, and on many a dark night poachers could be found somewhere on the river in pursuit of the salmon. This state of affairs continues unchanged for many years, until a local schoolmaster, Adam Horsburgh, decides that the Act should be challenged openly and a full scale salmon war breaks out. When poaching gangs from the cities, Berwick-for-Scotland enthusiasts, and even the Royal Navy join in, Adam begins to have second thoughts--but by then things have gone too far....