Batman: Detective No. 27 is an Elseworld comic, set more or less in The Golden Age of Comic Books, where Bruce Wayne never becomes the Batman, but is instead Detective No. 27 in the Secret Society of Detectives.
It is worth noting that the character of Batman first appeared in Detective Comics #27.
This graphic novel provides examples of:
- Animal Motifs: Unsurprisingly, bats are all over the place.
- Historical Domain Character: Quite a few.
- Jekyll & Hyde: The Trope Namer makes a cameo.
- Lawyer-Friendly Cameo: When Bruce Wayne is inducted into the Secret Society of Detectives, apart from Alfred and the Crimson Avenger, none of the other members are named, but from the way they're drawn, they're clearly intended to include Sam Spade (or maybe Philip Marlowe), Hercule Poirot, Nick and Nora Charles, and Nero Wolfe, amongst others.
- Massive Multiplayer Crossover: Aside from the usual Batman crew, we have Superman, The Crimson Avenger, Mr. Hyde, and detectives in the Secret Society who look a lot like Sam Spade, Nick and Nora Charles, Nero Wolfe and Hercule Poirot.
- Mythology Gag: Lots and lots. Babe Ruth calling Bruce "the Bat-Man" being the most obvious.
- Batman first appeared in Detective Comics #27.
- Babe Ruth says that if Wayne is "Detective 27", then he's "All-Star 3" - All-Star Comics #3 was the first appearance of the Justice Society.
- Joe Miller's Joke Book.
- Bruce mentions how he called Robert Frost "Mr. Freeze" when he was a boy.
- Catwoman dressing up as an old lady and Bruce recognizing her legs, as in her original Golden Age appearance.
- When Bruce is under the influence of Datura spores, he hallucinates Jonathan Crane becoming the Scarecrow.
- "As if in answer, a huge bat flies through the open window..."
- Jack Napier from the Tim Burton films shows up as Joe Chill's partner. The question "Have you ever danced with the Devil in the pale moonlight?" is also significant.
- "Do you envision yourself as some noble, dark knight, detective?"
- Bruce calls the Secret Society the Justice Society, and gets corrected.
- Navel-Deep Neckline: Catwoman's outfit has a plunging neckline that reaches her navel.
- Parental Betrayal: Thomas Wayne is revealed to be a supervillain who faked his death.
- Wham Line: "Didn't anyone ever teach you not to be so certain about life? And here I always assumed you'd be as bright as me... Son!"