Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
Third Person Limited Omniscient
The Man of Law is one of Chaucer's most present narrators. What do we mean by that? Well, the lawyer rarely misses an opportunity to comment on the action. He's all up in this story.
When Custance must travel to Babylon, he asks us "What wonder is it thogh she wepte?" He criticizes the Sultan's mother's scheming, calling her "feyned woman" and "nest of every vice" (362, 364). The narrator makes it very clear that he's firmly on the side of Custance. Any character who does her wrong is generally painted as evil.
It's worth pointing out that the Man of Law also uses the events of the tale to expound upon his belief that people have no control over what happens in their lives. He believes that the fates of men are written in the stars, and we are powerless to stop the suffering that inevitably follows joy. The narrator acts like a guide to how to interpret the events in the "Tale," making clear the lessons he thinks we ought to be learning as it progresses.