The Key to the Castle — Tony Nash

Bill Hallorane, brilliant seaman though he is, has always had to play second-fiddle to Alan Todd, and it rankles. A disastrous drinking bout and a resultant fire on their ship sees Hallorane fired, and he wants revenge. By pure chance, he meets up with one of the crew of their old submarine, which is mothballed in a Scottish loch, and with others of the original crew they steal it, with the intention of using it to threaten Todd's ship and steal the gold bullion it carries. Fate, as always, waits in the wings.