...with a look back at Detective Comics #300 and #400, with the adventures of the classic Silver Age Batman and Robin!
Detective Comics 300
Yes, Batman and Robin fight a villain who bases his crimes around polka dots. Surprisingly, Mr. Polka-Dot gives the Dynamic Duo a bit of a run, capturing Robin and eluding Batman, until Batman finds Robin, and the duo beat Mr. Polka-Dot at the location of his next crime. Even more of a shocker, this villain returned (but not for long; he's one of a long line of villains people try to forget).
Martian Manhunter, who debuted in Detective Comics was still a feature in the comic at the time, as was a short lived Aquaman feature, having transferred over briefly from Adventure Comics as his own magazine was just starting.
Detective Comics 400
This issue introduced readers to Dr. Kirk Langstrom, who had a fascination with Batman, and with Chiroptera (bats). While Batman was having some trouble stopping the Blackout Gang (a group of thieves who used technology to see in the dark), Langstrom was working on a formula to give himself night vision (basically, vision like a bat's). Langstrom did get sonar abilities, but he also got a bit extra, changing into a half-man, half-bat creature.
Man-Bat would return, and more of his exploits are detailed here, as he would get his own feature for a time after a few more times fighting Batman, including two issues of his own, and back-ups in Batman Family and Detective Comics (and it is well past time that all these tales of the Man-Bat were collected in one volume for readers, though most of the earliest tales have been collected, including this one).
Gotham Librarian Barbara Gordon headed to Hudson University to take advantage of their library, and quickly found herself (or, her alter ego, Batgirl), involved in trying to solve the murder of Amos Willard (with a student quickly caught, but she, as well as Dick Grayson, believed this boy was innocent). At the end of this tale, Batgirl was being sealed behind a wall....but, thankfully, the tale continued to the next issue, when Robin finally appeared, and the duo captured the real culprit.
Action Comics passed these milestones too, and there's still quite a ways to go to get to Detective Comics #1000!