The nun's priest, Sir John, is called upon by one of the pilgrims to tell a happy story since he feels such things are "gladsome" and beneficial to all.  So, the priest, who is the servant of the Prioress, apparently a maudlin, silly woman, seems to have a rather low opinion of the women around whom he is forced to live at the convent as he tells his tale of the handsome rooster Chanticleer.

This Chanticleer is a beautiful fowl surrounded by hens, who are like sisters to him.  Among them is a beautiful hen that he loves named Pertelote.

He loved her so that all was well with him.
But such a joy it was to hear them sing,
Whenever the bright sun began to spring,
In sweet accord, (ll.46-49)

Chanticleer loves her so much that he listens to her rather than heed his portentous dream of a yellow-red creature with black-tipped ears making "a feast upon [his] body." But, Pertelote dismisses his fears as indigestion and suggests that he eat some herbs. Chanticleer then illustrates the importance of dreams with an example of a man who awoke from a dream that his friend called out to him that he would be murdered, and the dream was fulfilled. The man, who had returned to sleep, awoke in the morning and went to the place his friend had slept and found him gone.  He searched for his friend in a cart covered with hay as he had dreamt and found the man dead.  In line 172, Chanticleer exclaims,

“O Blessed God, Who art so true and deep!
Lo, how Thou dost turn murder out alway!

"O Blessed God" is an example of apostrophe because it is an address to a being who is absent as though he is present and able to respond to the address.