After the Second Nun's tale, the group of pilgrims had barely ridden five miles, when a man dressed in black and his servant caught up with them. Chaucer guesses that the man was a Canon and was accompanied by his Yeoman. Both the Canon and his Yeoman seemed friendly and courteous. The Host welcomed them into the group and asked them whether they had any tale to entertain the pilgrims. The Yeoman replied that his master knew lots of fun and games. The Yeoman then launched into a huge praise of his master and proclaimed that he was a man of superior intellect. The Host then pressed the Yeoman to reveal more about his master's arts. The Yeoman readily answered that they lived in the suburbs and lived in anonymity like robbers. On being questioned by the Host about the discoloration of his face the Yeoman replied that probably the constant blowing into a hot furnace was the cause. When the Yeoman proceeds to reveal dark secrets about alchemy, the Canon threatened him of dire consequences. But the Host tells the Yeoman not to care about the Canon's threats. When the Canon realized that the Yeoman was going to reveal all his secrets he flees away in shame. The Yeoman then goes on to bare all the foul secrets about alchemy and vows that he shall never have anything to do with the Canon.
In the first part the Canon's Yeoman tells about his own experiences with his master while he is practicing alchemy. He expresses regret at having wasted seven years with the Canon since he hasn't gained anything. Rather his once fresh complexion has become sickly and his eyes have become weak. The wretched science of alchemy has stripped him bare and plunged him into such a deep debt that he will never be able to repay it. The Canon's Yeoman gives a detailed account of the alchemy processes and the abstract technical jargon involved. He denounces the vocation of alchemy and warns everybody from entering into it. He describes how when every experiment fails the blame is apportioned to some insignificant cause while the Philosopher's stone (the precious metals) remains elusive.
There once lived a deceitful Canon in London who was unsurpassed at double-dealing. One day this Canon entreated a chantry priest to lend him a certain sum of gold and promised to repay him by a certain date. The priest promptly lent him a gold mark. When the Canon returned the sum on the third day the priest was extremely pleased and said that he hadn't expected to ever see the money again. The Canon offered to repay the priest's kindness by demonstrating his expertise in alchemy. He told the priest to fetch him some mercury and charcoal. He then tricked the priest into believing that the mercury had been transformed into silver. He asked the priest to pile the charcoal for the experiment in the crucible. While the priest was thus occupied the sly Canon slipped in a piece of counterfeit beech wood charcoal in which he had placed an ounce of silver fillings. When the charcoal was burnt the silver fillings fell into the crucible. The poor unsuspecting priest had no idea that he was being duped. The Canon asked the priest to fetch a piece of chalk - stone to fashion a mould and went with the priest to convince him of the veracity of the experiment. The Canon then deftly took out a thin sheet of silver from his sleeve folds and cut the chalk stone to its size. He then hid the silver back in his sleeve. Then he took hold of the burnt beech charcoal and poured it into the mould and threw it into a vessel filled with water. He asked the priest to look for silver in the mould. The gullible priest was only too happy to find a bar of silver. To remove any trace of doubt whatsoever the Canon then offered to let the priest have a second try. He asked the priest to get another ounce of mercury and to repeat the experiment. The deceitful Canon in the meanwhile took out a hollow stick filled with one ounce of silver and tightly sealed with wax and threw it into the fire. The heat melted the wax and the silver ran out into the crucible. The Canon then told the priest to get some copper and tricked him for the third time into believing that it had been transformed into silver. The priest was extremely overjoyed and had the silver tested by a goldsmith. The priest then begged the Canon to sell him the formula. The Canon promptly sold him the fraudulent formula for 40 pounds and requested the priest to keep the matter a secret and cunningly left town the next day. The poor priest could not do anything when he realized that he had been duped by the Canon.
The Canon's Yeoman then proceeds to denounce the wretched vocation of alchemy and the complicated jargon involved and says that it only transmutes happiness into misery.
The Canon and his Yeoman arrive panting and gasping for breath after the main group of pilgrims when the journey is nearing its end. Their arrival is an attempt by Chaucer to introduce a new dimension in the relationships that have already been established among the pilgrims. The Canon practices alchemy. The main idea of alchemy is that certain basic metals lying in the ground for several years would eventually become higher metals. The alchemists claimed that they could accelerate this process.
The Canon's Yeoman's Tale is by and large an autobiography of his own experiences with his master practicing alchemy. The tale is in the form of a dramatic monologue. The Canon's Yeoman gives details of alchemy processes that may seem complex to the modern reader. However this also reveals that the Yeoman is extremely knowledgeable about alchemy. He knows all the technical terms and jargon. The Yeoman then relates a series of anecdotes about how another Canon cheated a priest into believing that he could transmute mercury into silver. It is evident that the Yeoman is disgusted with alchemy.
The Yeoman hates to be involved in such a hopeless occupation. He is incensed that he has lost his money and his good complexion. His wrath tends to increase by degrees as he tells his story. But it is important to note that the Yeoman does not condemn the science of alchemy itself. He only castigates greed and false crooked alchemists. He believes that one day they would learn the secret and discover the Philosopher's stone but only when God wishes them to do so. The story does not hold much appeal for the readers today as this concept of alchemy became outdated within a very short period of time.