Detective Comics #48 (February 1941)

It's worth noting that the Batman icon in the upper left-hand corner of the cover has been finally changed to resemble the current Kane/Robinson Batman with the shorter ears and blue highlights, rather than the Kane original it has been representing since #32.

"The Secret Cavern"
Writer: Bill Finger
Pencils: Bob Kane
Inks: Jerry Robinson and George Roussos
Synopsis: In Kentucky, a man idly rowing his boat down a stream ends up floating into a mountain and discovering a vast limestone cave, which just so happens to pass directly under the federal gold vault at Fort Knox! (cue dramatic music). He rushes back into town and blabs about his discovery to a bunch of guys in a bar, who of course turn out to be criminals on the lam. They recognize the gentleman as a millionaire named Lewis, who does spelunking as a hobby. When he refuses to tell them where the cave is, they kidnap him and threaten him. One of the criminals remembers he has a daughter named Linda who is a nightclub singer in Gotham City. One of the crooks, Nick, meets with the club's owner, Renaldo, and convinces him to join in on the scheme.
That night, Linda is seeing Bruce Wayne at the club (uh, Bruce, aren't you still engaged to Julie Madison?), and after she sings she makes a date to go to the movies with him. But when she retires to her dressing room she is startled by a man waiting for her who attempts to grab her. She takes a gun from her dresser and shoots him. Renaldo bursts in and announces that she has killed the man. Scared, Linda agrees to flee to her father in Kentucky with Renaldo's help, while he covers up the murder.
But of course, no one has died. The man she shot was Nick, who replaced the bullets with blanks. It was all part of the plan. Back in the club, Bruce questions Renaldo as to where Linda is, but is told off. Bruce begins to suspect something has gone wrong.
Linda arrives in Kentucky by train, and meets Renaldo there. Her father has been told about Linda "murdering" Nick, and agrees to rell Renaldo and the crooks about the cave's location in order to keep the "murder" quiet and keep Linda out of prison. 
Meanwhile, Bruce continues to be suspicious of Linda's sudden disappearance. "She worked for Renaldo, Renaldo went out of town, she went out of town, it all adds up!" Okay, sure thing. Anyways, Bruce gets Dick in on this, and as the Dynamic Duo they rush down to the abandoned barn and burst onto the scene in the... Batmobile! Actually, it's the same red 1936 Cord they've been driving this whole time, but Finger is calling it the Batmobile in the narration for the first time. 
They drive to Renaldo's apartment, hoping to find some clues as to Linda's disappearance. There they discover a crook talking on the phone with Nick, reminding him to lay low. Batman and Robin burst in, and Batman beats the crook into giving them Nick's location -- a garage that fronts a gambling joint. Back in the Batmobile, the Dark Knight realizes he was in such a rush that he forgot to tie the crook up, who is now phoning Nick and warning him of the Batman's approach!

So knowing that the element of surprise is lost, Batman simply RAMS into the garage with the Batmobile! Batman and Robin brutally beat up the gangsters and capture Nick, who reveals Renaldo and Linda's location in Kentucky. The Dynamic Duo journey there in the Batplane, arriving at the Lewis cabin. Batman makes his entrance via the best knock-knock joke ever. (Image courtesy of Chris Sims).
 Batman then proceeds to introduce Linda and her father to Nick, the man she "killed". But it's too late, Lewis has already told the crooks about the cave, and they're already on their way there!
Batman demands that Lewis take the Dynamic Duo to the cavern, so that they may stop the criminals. Rowing down the stream through the limestone cave, the Dark Knight and the Boy Wonder comment on the awesome solemnity of the place -- you can almost see the thought balloons of "gee, why don't we have a cave? These things are great!"
Meanwhile, the crooks have finished digging up into the vault, but are being spooked by bats from the cave. So of course, Batman steps out of the shadows and kicks their asses. The fight brings the National Guard down on them, who shoot all the criminals and offer Batman and Robin commendations for medals of bravery! The vigilante Batman refuses however, saying that "being Americans is enough of an award!" Wow. Well, I guess it is January, 1941.
My Thoughts: This is a fantastic story that really showcases a team working at the top of their game. Finger, Kane, Robinson, Roussos, they all deliver here. The tale itself is pretty standard comic book, but its the effort and care being put into the story that makes this a Batman comic not worth missing. The only thing about it that's a little odd is the US Soldiers offering Batman, a wanted vigilante, a medal. But pretty soon I guess I'm gonna have to get used to patriotic flag waving.
The Art: The art is GORGEOUS! It's the absolute BEST it's been since Detective Comics #38, I kid you not. It's got Robinson's detailed inking alongside Roussos' solid black swaths of shadows, and Kane's layouts are dynamic and engaging. It's seriously the artwork that elevates this story. You need to see it. Go out and buy "Batman Chronicles Vol. 3" right now, damnnit!
The Story: Finger's story is pretty good, but it's not his best. What's nice about it though is the pacing. Nothing feels especially rushed, like how most Golden Age stories feel. And given that it's gonna be another fifteen years or so until Ian Fleming writes Goldfinger, this is a pretty good "rob Fort Knox" scheme. What's great here is that there's beginning to be a distinction between the way Batman and Robin are written -- with the daredevil attitude and joke-y quips being Robin's forté and Batman being a brutal and determined avenger of crime. Good stuff.
Notes and Trivia: First time Batman's vehicle is referred to as the "Batmobile".