When Ray Palmer and Jean Loring attend a masquerade party, they come across a guy who is drawing crowds by dressing up as a 20th century version of the Man in the Iron Mask. As he wins the costume contest, he proceeds to cause a blackout with his glowing mask. When the party attendees regain their conscious, they realize that they were robbed. Ray investigates and detects ion radiation. After Ray uses an anti-ion ray on his suit, he goes to buy Jean a birthday present. At this same store is Ion Mask, who is attempting to rob it. The Atom and Ion Mask get into a scuffle, yet Ion Mask is able to escape. Ray realizes that out of all witnesses interviewed, there was one man who appeared both times: Ed Jameson. Ray decides to follow Ed in order to find out where Ion Mask will strike next. Just as Ray predicted, Ion Mask showed up to rob the box office at the horse betting track that Ed was at. The Atom manages to defeat Ion Mask and pulls off the mask, which to much of Ed's surprise is his brother Bill. Bill reveals that he was working on an Ion ray that could only work when near Encephalonic waves, which Ed's mind was producing. Bill also revealed that the ion mask caused blackouts by affecting the cerebellum of the brain.