Following his battle with Azmodus in Showcase #60, The Spectre must fight Shathan the Eternal, the embodiment of evil. Shathan offers to save the lives of humans in mortal peril in exchange for their shadows. These shadows he corrupts and implants back into their hosts' minds to create a body of worshippers on Earth that will strengthen his power and allow him to break through the titular "sinister barrier" that separates Earth from his realm, the evil nether universe of psycho-matter which contains Shathan's home world, Dis.
Drawn by ecto-plasmic magnetism into the body of one of Shathan's unwitting followers, The Spectre fights the man's shadow, before being transported to Dis where he is nearly overwhelmed by the evil denizens there.
Following instructions from a voice (possibly The Voice), The Spectre travels back in time 12 billion years to the moment of creation when the Primal Atom exploded creating both the matter universe and the psycho-matter universe. There he learns the origin of Shathan, and returns to Earth where he alone can stop Shathan. The Spectre even speculates that, stopping Shathan is, "Perhaps the very reason why The Spectre was brought into existence years ago."