The Story: "History-Making Costumes of the Royal-Flush Gang!" by Gardner Fox, Mike Sekowsky, and Sid Greene. Hal Jordan lays dying, and the clues to who do it lead to crooks dressed as historical figures like Queen Elizabeth and Alexander the Great! Turns out it's actually the Royal Flush Gang, so you've got people wearing costumes inside other costumes.
Roll Call: Batman, Wonder Woman, Flash, Martian Manhunter, Atom
Notable Moments: Flash visits Hal Jordan in the hospital, and immediately lays his hand on the power ring so it can telepathically tell him what happened to his friend. They don't really explain that, which I thought was a nice, subtle touch of characterization--Barry and Hal are close friends, so Barry knows how the ring works.