Finley's (P) husband and two children were flying in a twin-engine plane when it struck electrical transmission lines on its approach to a San Diego airfield. They were killed in the crash. P sued San Diego Gas and Electric Company, and the city of San Diego in state court. P later discovered that the FAA was also to blame and sued them in federal court on the Federal Tort Claims Act (28 U.S.C. section 1346(b)). Almost a year later, she moved to amend her federal complaint to include claims against the original state court defendants as to which no independent basis for federal jurisdiction existed. That motion was granted by the District Court upon a finding that judicial economy and efficiency favored trying the actions together as they arose from a common nucleus of operative facts. The Ninth Circuit reversed, and the Supreme Court granted certiorari.