heavy machinery / complex system / machine

(literary) deus ex machina (suddenly, unexpectedly, and without prior indications)

(Ancient Greece, Ancient Rome, drama, historical, literary) deus ex machina (plot resolution in ancient tragedy involving the sudden and unexpected appearance of a deity) / (Ancient Greece, Ancient Rome, drama, historical, literary) deus ex machina (deity in Greek and Roman drama who was brought in by stage machinery to intervene in a difficult situation) / (literary) deus ex machina (unexpected saviour) / (literary, narratology) deus ex machina (contrived plot resolution)