The Secret of Boyne Castle (television title) or Guns in the Heather (theatrical title) is a wild romp through late 1960's Ireland with two school chums being pursued by spies from an unknown state. The story opens with an automobile chase scene of a mortally wounded Irish underworld figure being chased by the spies. The chase ends at an upper class school where the spies will not of course follow the man they wounded onto the school grounds. The wounded man is looking for an American student at the school by the name of Rich Evans. With his dying breath, he tells Evans to look in, "...my room at Boyne Castle." Rich with his friend Sean O'Connor set off for Boyne Castle but on the way are kidnapped by the spies. They seem to feel that Evans knows something that his older brother Tom - who unbeknown st to Rich Evans is a secret agent - knows. The indignant younger Evans replies, "...Tom's a sales representative for steel company." Evans and O'Connor manage to escape from the "bad guys." Here is where the real fun begins. With the Irish countryside and highway system as a backdrop, a cross-country chase ensues of Evans and O'Connor being pursued by the spies. While continually getting into and then out of scrapes with them, Evans and O'Connor use considerable ingenuity to evade their pursuers. In one instance they attack their pursuers by dropping cannon balls from a glider. All the while Rich is wondering what his brother Tom's involvement in all this is. The "secret" of course lies at Boyne Castle.