Whilst on a publicity visit to the southern states President William B. Sheridan was assassinated. A journalist, with dramatic flair, dubbed it "The Day of the Black Sun".

By chance an amateur cameraman at the scene caught the killer on film. He was later identified as Captain Steve Rowland, an officer of the elite SPADS unit who was officially reported missing on active several years earlier.

Colonel Amos, leading Judge Allenby's investigation, located Rowland who had lost his memory as a result of a bullet wound to the head. The only clue to his former identity was the roman numeral XIII tattooed above his left collar bone.

Proving himself to be a highly trained man of action, the amnesiac escaped from Amos' grasp and returned to, what he believed to be, his family. Here he fell prey to the schemes of his, all too seductive, step-mother who framed him for the murder of his "father" and "uncle".

Escaping once again he tracked down the woman who he believed to be the key to his former identity: Kim Rowland, wife of the Presidential assassin. From her he was able to learn that the real Rowland was truly dead.

In addition, Kim also carried a similar tattoo on her left shoulder. Was this the mark of the members of a conspiracy whose goal was to assassinate Sheridan?

Before he had time to discover more XIII was arrested and convicted of the murder of his "parents" and sentenced to life, without remission, in the prison wing of the Plain Rock Asylum.