Final answer:
In "Masque of the Red Death," the uninvited midnight guest symbolizes death itself.
Step-by-step explanation:
In "Masque of the Red Death," the symbol that represents a deadly plague or death itself is the uninvited midnight guest. This character, described as having a corpse-like appearance and wearing a mask resembling the Red Death, is the embodiment of death. The presence of this guest at Prince Prospero's masquerade ball signifies the inescapability of death and the futility of trying to avoid it.
Learn more about symbolism in literature