The Seance's Double Locked Room Mystery (Opening of the Locked Room)

Mouri, Ran, and Conan are attending a play when Conan overhears one of the actor's murder plan. He is later found eaves dropping and placed in a coffin. Later he over hears the other two actors who also plan a murder, meaning a murder triangle has been formed. After they seemingly all die, Conan is revealed to manage to save all of them having escaped from the coffin through a back door.