You are packing up after a week-long stay at the Verity Inn. You came here, to Truth Town, to visit your friend but now it's time to go home. You feel in good spirits as you pack your bags. As you are leaving, however, your good mood vanishes when you are approached by the city's guild-master who asks for your help.
"The knight and knave who stand at the crossroads between here and Liar-ville have started causing even more confusion for travellers. It's bad for business! The one has cursed the other one to answer... differently -- and I don't know which -- so I need you to take this curing potion to them and give it to the cursed one. They need to go back to the way they were so that people have a better chance of finding the correct road."
You have to pass by on your way home anyway, so you accept the potion and a leaflet containing further instructions, and leave.
As you approach the fork where the knight and knave are standing, you see that they still look identical. You remember that the one always tells the truth and the other one always lies. You wonder what the curse did that makes this any harder than before? So you read the leaflet of instructions.
Oh dear. Things seem to have gotten a bit out of hand.
They are able to say no more than "yes" or "no".