Great cover for the debut of the Cluemaster, in Detective 351 (May 1966). The story itself, by Gardner Fox, with art by Infantino and Greene, gives the largest role to Aunt Harriet that the character will ever get.
The story opens as she accidentally discovers the elevator to the Batcave. She even goes down and explores it. She hints to Bruce and Dick about her discovery, but they have already covered their tracks. She spends the rest of the story trying to prove they are Batman and Robin.
Meanwhile, the heroes are dealing with the Cluemaster. He’s basically the Riddler, except his clues are not in the form of riddles.And though Batman and Robin do not realize it at first, he is also seeking the Batcave, and the secret of their identities.
The two plotlines converge when the traps Cluemaster and Aunt Harriet have laid wind up exposing each others traps, so Bruce and Dick have plenty of time to figure out how to outwit both.
And sure, Cluemaster is left in the dark, but the film they create for Aunt Harriet is hardly a solution, showing her that Batman and Robin do indeed have a cave under the mansion, and are in contact with Bruce and Dick. That’s just bound to create bigger problems later on. Or would, if Aunt Harriet hadn’t been such a marginal character.
As for Cluemaster, it took until the 90s for this character to come to life. He has a number of cameos before that, the next one in a Batman comic from 1968.
It’s just Fox and Infantino on the Elongated Man story in this issue. Ralph has plans to donate his old costume to the Flash Museum in Central City, but discovers that it has been stolen.
It turns out his costume has retained some of its elasticity, and is being used, basically as a giant rubber band, by a clever crook, to facilitate his escapes.
Old vs new for the climax, and of course Ralph wins. The Flash has a cameo at the end of the story, as Ralph and Sue present the costume to the museum.