A precious golden souvenir has disappered from Kismuil Castle in the Island of Barra. The historic brooch was given as a gift by the Chief of Clanranald to MacNeil of Barra in the 16th century. Or perhaps it was treasure found from a shipwrecked galleon from the Spanish Armada... Tha local constable, P.C. Murdo, sets out to find out whodunit. He has seven suspects, but in his search for the truth discovers that suspicion and prejudice make poor detectives. Help comes from smart officers from the mainland, whose most difficult challenge is Murdo himself.