"The fee is three true things," said the ferryman.
"Agreed!" said the wolf.
As they set sail, the ferryman asked for the first thing.
"He does good who is good," said the wolf.
Midway across the river, the ferryman asked for the second, and the wolf said, "He does bad who is bad."
"And the third?"
"Not yet," said the wolf.
Then, when they reached the other shore, the wolf leaped from the boat and shouted, "He who helps a villain like me is a fool!"
Inspired by: Mille Fabulae et Una, a collection of Latin fables that I've edited, free to read online. I am not translating the Latin here; instead, I am just telling a 100-word version of the fable.
Notes: This is fable 74. Lupus et Nauta in the book, which is Perry 687, from the Romulus Anglicus. I changed what the wolf says since I couldn't quite catch the wordplay in the Latin.