Deus ex machina
"It is obvious that the solutions of plots... should come about as a result of the plot itself, and not from a contrivance, as in the Medea and in the passage about sailing home in the Iliad. A contrivance must be used for matters outside the drama—either previous events which are beyond human knowledge, or later ones that need to be foretold or announced... There should be nothing improbable in the incidents; otherwise, they should be outside the tragedy as, for example, in Sophocles' Oedipus.