Ex parte Reed was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner who was being held in federal custody. The case arose when a prisoner, William Reed, was arrested by federal authorities and held in federal custody. Reed then filed a petition for a writ of habeas corpus in a state court, arguing that he was being held in federal custody without due process of law. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to detain a prisoner. The Court also noted that the writ of habeas corpus was a remedy that could only be used to challenge the legality of a prisoner's detention, and not to challenge the merits of the underlying criminal charge. In conclusion, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to detain a prisoner.

In Ex Parte Reed, the Supreme Court was tasked with determining whether a state court had jurisdiction to issue an injunction against a defendant in another state. The majority opinion held that the lower court did not have such authority and reversed its decision. Justice Field dissented from this ruling, arguing that the lower court should be allowed to exercise jurisdiction over defendants located outside of their own state when necessary for justice's sake. He argued that while it is true states are generally limited to exercising power within their own boundaries, there may be cases where it would be appropriate for them to do so if they can demonstrate good cause or necessity. Furthermore, he noted that Congress has granted some courts express permission to take action beyond their borders in certain circumstances and thus found no reason why similar allowances could not also apply here as well. Ultimately, Justice Field concluded by asserting his belief that allowing states more flexibility in these matters would help ensure fairness and justice across all jurisdictions regardless of geographic location or political affiliation.