Thatcher's Son Charged in Coup Plot CAPE TOWN, South Africa - Mark Thatcher, the son of former British Prime Minister Margaret Thatcher, was arrested Wednesday and charged with helping to finance a foiled plot to overthrow the government of oil-rich Equatorial Guinea.    Thatcher, a 51-year-old businessman who has lived in South Africa since 2002, was arrested at his Cape Town home shortly after 7 a.m...