Syfy has unveiled a new trailer for the Superman prequel series Krypton, which finally reveals the main plot.

Set 200 years before Superman’s birth, the story is told from the perspective of Kel-El’s teenage grandfather, Seg-El. Then Adam Strange, a human archeologist, shows up on Krypton with a dire warning, someone from the future is coming to alter the timeline, so Kal-El is never sent to Earth.

The series premiers on Syfy on March 21.

Syfy has been ramping up the publicity for the show. It recently released promo shots of the main characters (see “New Promo Images for 'Black Lightning,' 'Krypton'”).