I have two books by Raymond Smullyan that are all "one of us only lies, the other only tells the truth" type puzzles.
In this puzzle on the island of knights and knaves, knights are unavoidably honest and knaves always say contrary things. I was visiting the island when I saw three strangers (A, B, and C) spending time in a garden. As I approached the group, I asked A "If you don't mind, are you a knight or a knave?" A obligingly answered but I wasn't close enough to hear, so when I got closer I asked B "what did A say?" B said "A told you he's a knave," but C interrupted to say "Don't believe B, she's lying." Can you figure out the knight/knave status of B and C?