State immunity — Jurisdictional immunity — Whether presumption of sovereign immunity — Individual acting in official capacity on behalf of Government — Commercial activity exception — Distinction between sovereign and commercial act turning on nature rather than purpose of act — Lack of profit motive — Whether creating presumption of sovereign act — Kidnapping of plaintiff in Mexico — Kidnapping allegedly arranged by Mexican Government official in order to curry favour with Mexican businessmen — Whether constituting a commercial activity — Whether kidnapping falling within non-commercial tort exception — Requirement that tortious acts be committed in United States — Requirement that tortious acts not committed by foreign State in the exercise of discretionary function — Extent of exception regarding immoveable property — The United States Foreign Sovereign Immunities Act 1976 — Whether conferring immunity on wife of Head of State — The law of the United States