Watch Alien: Covenant - Prologue: The Crossing for Free: How to Stream the Movie Online at 123Movies. . Aboard a hijacked Engineer vessel, Dr. Shaw repairs David as they make their way to the home-world of the Engineers, whom Shaw believes are humanity’s creators. 'The Crossing' is an official prologue short to 'Alien: Covenant', revealing what happened to crew members Dr. Elizabeth Shaw and the synthetic David after the events of 'Prometheus'.