The two then plotted to kill the wolf with knives and stalked him to his cave.  But the wolf pounced on them: Chang Nan ran away and his wife was stripped bare.  At the commotion, Chang Kuo woke up and saw his naked sister-in-law flee screaming for her life.

The third attempt was different.  The brother and sister-in-law went to the magistrate and had Chang Kuo arrested for killing Chang Nan’s pigs.  He was held, convicted, and beaten.  When he returned to the cave he found that the evil duo had killed the wolf.  Chang Kuo was distraught.  He could not eat or sleep for days.  Eventually, out of sheer exhaustion, he fell asleep.  But even in death the wolf was determined to help and spoke to Chang Kuo in a dream:  “There is a unicorn in a valley near here that can travel a thousand li [over three thousand miles] in a single night and two thousand more during the day.  If you can catch this unicorn, it will make you an immortal.”

Chang Kuo awoke with a start and ran to the valley.  But whenever he approached the unicorn, it moved away.  When he chased it, the unicorn ran with the speed of an eagle.  So Chang Kuo practiced running.  Eventually, he could run for days without tiring, but his shoes always wore out.  So he asked a blacksmith to make him shoes of iron.  To his surprise, the smith knew of his quest: “You are Chang Kuo, the friend of the black wolf.  You are trying to catch the unicorn, aren’t you? I can give you something that will help you more than iron shoes.”

The blacksmith drew a picture of a donkey on a piece of paper.  Chang Kuo protested that donkeys are slower than unicorns and a donkey made of paper slower still, but the blacksmith answered: “This donkey can run as fast as the unicorn.  Just watch.”

He laid the paper donkey on the ground.  It began to shake, then a live donkey jumped up.  As it galloped out of the blacksmith’s shop, Chang Kuo leaped on it.  But just at that moment the donkey reversed direction, and Chang Kuo landed astride but facing backward.  Chang Kuo held on in this position as the donkey raced toward the valley of the unicorn.  At the sight of the strange duo, the unicorn jumped high into the sky, and, to Chang Kuo’s amazement, the donkey followed.