You can never get enough secret origins! That was DC's thinking, at least.
The startled JLA (plus Robin) are about to be told the stories:
"The Case of the Real Gone Flash" by John Broome, Carmine Infantino, and Joe Giella
"The Amazing Bizarro" by Otto Binder and George Papp
"The Day 100,000 People Vanished" by Broome, Gil Kane, and Giella
"The Mad Hatter of Gotham City" by Bill Finger, Sheldon Moldoff, and Charles Paris
and the classic "Slave Ship of Space" by Gardner Fox and Mike Sekowsky
...when I was a kid and bought comics on newsstands, the budding collector in me couldn't stand when the sale date of the book was stamped on the cover, as this one is. Now I look at it as a charming reminder of days gone by.