Board Thread:Questions and Answers/@comment-918732-20160414155022/@comment-1257201-20161006183142

Etrigan -- Actually, that is the correct answer! The synopsis on this site is incomplete for that story.

In, Feb. 1976, Batgirl (Barbara Gordon) and Robin (Dick Grayson) discovered each others' secret identities. Logically, this meant that Barbara could easily deduce Batman's identity as well, but Robin chose not to inform Batman of this development.

In, April 1980, Batgirl was hooked up to a mind-erasing machine for dubious plot reasons. At the end, when her memory was being restored, she and Dick agreed that her knowledge of Batman's and Robin's identities should not be included in her memory, in order to safeguard their secret.

In, June 1981 -- at least, I'm pretty sure it was this issue -- Batgirl needs help from Robin, and knocks on Dick Grayson's window. He says, "I didn't think you knew our identities. I thought Batman and I threw you off the scent some time ago." (This was writer Gerry Conway's way of alluding to the earlier story without bringing up the ridiculous details.) She replies, "I'm a detective, remember?" A great reply!