Amelia Pelkes owned shares of stock in Sunshine Mining Company (Sunshine) (plaintiff). Amelia died intestate, and her probate proceedings occurred in Washington state court. The Sunshine shares passed to Amelia’s surviving husband, John Pelkes, and also to Amelia’s daughter from a previous marriage, Katherine Mason (defendant). Pelkes and Mason came to a private understanding about the stock, and Pelkes later transferred all of the shares to Evelyn Treinies (defendant). Mason filed suit in Idaho state court against Pelkes and Treinies, seeking one-half ownership of the stock. Treinies personally appeared in the Idaho action. Before the Idaho action was resolved, Mason also filed an action in Amelia’s probate proceeding in Washington state court, seeking to remove Pelkes as the executor of Amelia’s will. Pelkes filed a counterclaim asserting ownership of the Sunshine stock, and Mason sought a writ of prohibition from the Supreme Court of Washington. Mason argued that the Washington probate court lacked jurisdiction over the question of the stock’s ownership. The Supreme Court of Washington denied the writ, and the probate court entered judgment upholding Pelkes’s full ownership of the stock in May 1935. In August 1936, Mason won a final judgment against Pelkes and Treinies in the Idaho action. In response, Pelkes and Treinies filed an action in Washington state court seeking to quiet title in the stock. Pelkes and Treinies argued that the Idaho decree was invalid for lack of jurisdiction, and that the Washington court had already decided the jurisdictional issue by denying Mason’s writ of prohibition. Sunshine filed an interpleader action in federal district court to resolve the inconsistent judgments. The district court held that the Idaho decree controlled and upheld Mason’s ownership of the stock. The court of appeals affirmed, concluding that the Idaho court’s jurisdiction was res judicata in the interpleader action. The United States Supreme Court granted certiorari to review.