On vacation in the Scottish Highlands to visit his Uncle Michael (with Sally and Mildred in tow; Enright comes over later), Mac walks onto the grounds of the McMillan castle and shouts for Uncle Michael. The response is a rifle shot. Mac rushes in and finds Uncle Michael's lawyer and his housekeeper, who are trying to break into the "keep" which Uncle Michael uses as an office. Uncle Michael is dead on the floor, shot through the head with a rifle lying beside him. All the evidence points to suicide, but Mac won't believe it -- especially when two men run away from ...