Batman and Robin find a three hundred year old piece of pottery while digging a thing for some wiring or something. It's covered with Native American symbology that, when they bring it to an expert to be translated, reads as "Death to the man with two identities!"

Curious, they go to a professor who hypnotizes them and sends them back in time.

There they rescue a frontiersman from Native Americans trying to kill him and he takes them to his secret hide-out, a local cave he calls his Bat-Cave. It's there that he poses as a Native American by...

um

using the bark of a tree to dye his skin red.

Anyhow, he's been acting as a spy in their tribal camps, telling the local American general where the next attacks will be.

But he broke his leg when Batman and Robin rescued him, so they do stuff like set up primitive elevator to secretly bring his horse into the Cave so that it isn't spotted.

And create a periscope for him so he can see anyone trying to attack his, uh. Secret cave that no one knows about.

And...

Imagine just going to a dude's house after he's broken his leg and rearranging everything to be more efficient

And then assuming he'd want a trophy room

just gonna cut out bruce dropping some slurs here

again, they time travel by letting a doctor hypnotize them

it's always kind of funny to see Batman doing things like this, or sitting in on anti-crime committees or other formal legal stuff.