Mason v. Sargent 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 held in a federal prison. The case arose when a prisoner, Mason, was held in a federal prison in Massachusetts. Mason 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 power, and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not interfere with the federal government's power to protect this right. 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 power, and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not interfere with the federal government's power to protect this right.

Justice Field delivered the dissenting opinion in Mason v. Sargent, arguing that the majority's decision was an incorrect interpretation of the law and would lead to unjust results. He argued that a contract between two parties should be enforced as written, regardless of whether it is considered fair or not. In this case, he believed that there had been no fraud or mistake on either side when they entered into their agreement; therefore, it should have been upheld by the court. Furthermore, Justice Field noted that if one party were allowed to unilaterally change terms after entering into a contract without any legal justification for doing so then contracts would become meaningless and could not be relied upon by anyone seeking to do business with another person or entity. As such, he concluded that while some may consider this particular contract unfair due to its unequal division of profits between both sides involved in it did not give them cause enough to invalidate it under existing laws governing contractual agreements