The Court of Probate for Harford (probate court) invalidated the will of Normand Morrison, and, as a result, certain property vested in the Calders (plaintiffs). The Connecticut legislature then passed a law that set aside the decision of the probate court and granted a new hearing. The probate court approved the will on rehearing, divesting the property to the Bulls (defendants). The Calders appealed on the grounds that the new law was an ex post facto law and thus unconstitutional. The superior court and the Supreme Court of Connecticut ruled against the Calders, affirming the probate court. The United States Supreme Court granted certiorari.