Pit of Vipers (Nancy Drew) by Carolyn Keene

There's been a snake-napping at the River Heights Zoo, and all clues about the thief seem to point in my good friend Charlie's direction. But why would Charlie want to steal a snake? I'm not convinced he's the perpetrator, but with all the circumstantial evidence that keeps popping up, the cops are on the other side of the fence. Speaking of snakes, George's younger brother, Scott, has been slithering around a lot lately, all sneaky-like. He's not acting like himself, but his lips are sealed about what's wrong. Do these mysteries have anything to do with each other? Stick around. I'm about to find out!