Hancock v. Holbrook 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 a federal prison. The case arose when a prisoner, John Hancock, was held in a federal prison in Massachusetts. He sought a writ of habeas corpus from the state court, claiming that he was being held in violation of the Constitution. 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 a federal prison. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the power to interfere with the federal government's authority to detain prisoners. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's ability to protect the rights of its citizens. 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 a federal prison. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the power to interfere with the federal government's authority to detain prisoners. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's ability to protect the rights of its citizens.

Justice Field delivered the dissenting opinion in Hancock v. Holbrook, arguing that the majority had misapplied the law and misinterpreted a contract between two parties. He argued that under Massachusetts law, which was applicable to this case, an agreement made by one party to pay another for services rendered could not be enforced if it was found to be invalid or unenforceable due to fraud or mistake of fact. In this case, he argued that there were sufficient facts presented at trial indicating that such a mistake of fact existed when Holbrook agreed to pay Hancock for his services as an attorney; thus making their agreement invalid and unenforceable. Furthermore, Justice Field noted that even if no mistake of fact had been present in this particular instance, Massachusetts courts would still have refused enforcement based on public policy considerations alone since they do not enforce contracts which are deemed immoral or against public policy interests. Therefore he concluded with disagreement from the majority's ruling and urged reversal of judgment so as not to set precedent contrary to established state laws regarding contracts involving mistakes of fact or those considered immoral/against public policy interests