In the closing panels, we hear from the Outsider for the 1st time via telephone, but we don't see him.
Robin does not appear in this story.
Archive credits Joe Giella for the inks, but the Julius Schwartz editorial records provided by DC Comics says Sid Greene was the inker.
Biographies for Murphy Anderson, Bill Finger, Gardner Fox, Joe Giella, Sid Greene, Ed "France" Herron, Carmine Infantino, Bob Kane, Sheldon Moldoff and Julius Schwartz.
DC Archive checklist.