A person has been arrested and detained by the police without any lawful authority. To obtain his immediate release, the most appropriate writ is:

Explanation: Habeas corpus ('you may have the body') is the appropriate writ to secure the release of a person who has been detained unlawfully or without legal authority, whether by the State or a private person. It directs the detaining authority to produce the person before the court, which then examines the legality of the detention and orders release if unlawful. Mandamus compels performance of a public duty, certiorari quashes an inferior tribunal's order, and prohibition restrains an inferior court from exceeding jurisdiction. Habeas corpus is thus the direct safeguard against illegal detention.