You've seen The Exorcist. You've seen the movie about the making of The Exorcist, The Exorcism. Now, prepare to see the movie about the exorcists and the exorcism that inspired The Exorcist. Yes, David Midell's upcoming possession chiller The Ritual is set to see Al Pacino and Dan Stevens play real-life priests Theophilus Riesinger and Father Joseph Steiger, whose 1928 exorcism of Emma Schmidt — chronicled in Carl Vogl's controversial 1935 book Begone Satan! A Soul-tiring Account Of Diaboloical Possession In Iowa — served as the inspiration for William Friedkin's horror magnum opus. The power of Christ compels you... to check out the trailer below:

As possession horror trailers go, this one's certainly hitting all the well-worn genre grooves: talk of "the armour of God"; restraints, convulsions, and flinging furniture; distorted, unholy voices; and a couple of priests — one the wily old fundamentalist, the other a green young sceptic — experiencing the ultimate crisis of faith.