Byron starts off by saying that he needs a hero for a long poem he wants to write. It seems as though anyone will do, so he just chooses Don Juan (who was already an established character in Western history).
Byron starts off by telling us all about Don Juan's upbringing in the Spanish town of Seville. His parents are from good families and his mother is highly educated for a woman of her time. The problem with her is that she's a little too perfect, which makes her stuck-up.
Don Juan's father is more careless than his mother. The dad isn't really interested in learning or working hard. He just wanders around doing whatever he wants.
Their contrasting personalities eventually causes Don José and Donna Inez to fight. The speaker talks of how he tried to intervene and bring the two to peace, but it didn't work out.
With his parents fighting all the time and trying to make him take their side, Don Juan grows up as a spoiled child.
Donna Inez tries to get her husband put away by calling him crazy, but it doesn't work. The two are finally about to get a divorce when Don José dies unexpectedly. The death leaves Don Juan as the heir to a pretty decent estate.
With Don José gone, Donna Inez puts all her thoughts into making Don Juan the greatest person he can be. She hires all kinds of tutors to make him super-smart. She has trouble finding literature for him, though, because there's so much sex and violence in the classics. Don Juan ends up reading a lot of church sermons.
Over time, the tutors stamp out a lot of Don Juan's spoiled selfishness. By the age of twelve, he's a quiet and thoughtful boy. The speaker makes a personal note of saying that sending young boys away to school is usually better than homeschooling.
Next thing you know, Don Juan has turned sixteen and he is one of the handsomest young men you've ever seen.
One of Donna Inez's close friends is a woman in her mid-twenties named Donna Julia. This woman is married to a much older Spanish man named Alfonso, and she finds Don Juan's boyish looks refreshing. She tries to resist, but she feels a deep sexual attraction to him. She takes every opportunity to touch him when he's near.
One day, Julia decides to end things once and for all and to tell Donna Inez that they can't hang out anymore. She goes to Inez's house to deliver the news, but Don Juan opens the door.
Julia convinces herself that an affair with Don Juan will be okay because she'll be giving him a sort of sexual education.
Don Juan, in the meantime, doesn't understand the urges taking over his body. He starts spending a lot of time wandering alone in the woods and being philosophical. He knows that nature is trying to speak through him, but he's been so sheltered from sex that he doesn't understand what his body wants.
Here, the speaker suggests that Donna Inez knows all about Don Juan's budding affair with Julia. The speaker isn't sure why Donna does nothing to stop it. Maybe she wants her son to become a man or maybe she wants Julia's husband Alfonso to be humiliated.
In any case, Alfonso seems to get wind of what's going on with his wife.
We look in on Julia sitting alone at the edge of a cliff and thinking about how boring and old her husband is compared to the young and beautiful Don Juan.
Julia decides that she'll never dishonor her marriage vows by having sex with another man. But, at this same time, she unknowingly puts her hand on Juan's. It turns out that Juan is sitting next to her. Juan takes the hand and kisses it. The poet suggests that this leads to sex between the two.
Byron takes this moment to write satirically about English morality and its squeamish attitude toward sex. His basic argument is that English sexual taboos are lame. He then gives a sincere speech about how sex is awesome, especially when you have it for the first time.
Donna Julia is in her bed one night when her husband barges in with a mob of people carrying knives and pitchforks. Alfonso is convinced that Julia is seeing another man, so he and his gang search the room. They don't find anyone, though, and Julia takes the opportunity to give a huge speech about what a jerk Alfonso is.
The truth is that Don Juan is hiding in the sheets that are heaped up in Julia's bed.
Alfonso and his mob leave, but Alfonso comes back a few minutes later and finds Don Juan's shoes. Alfonso runs to get his sword and a scuffle ensues. Don Juan manages to get away and runs naked into the night.
The whole affair becomes a huge scandal in the local newspapers. Donna Inez decides to keep her son out of trouble by shipping him off to live somewhere else. She hopes that this traveling will also help him become wiser. Julia, on the other hand, goes off to live as a nun. We get a letter from her to Juan saying that she'll keep loving him.
To end his first canto, Byron goes off on another rant about how the public may see this poem as something that's immoral or dirty. He talks about all the poets who are respected in his time and says they're too boring and too "safe." He also tells his readers not to worry, because later in the poem he plans on showing hell in all its horror to remind people of what happens to those who are immoral.
Next, Byron talks about how reluctant his publisher was to publish this first canto at all. Now it looks like he's just thinking out loud.
Byron laments that fact that he's too old to be young and beautiful like Don Juan. He feels as though he has wasted his youth. In the end, he doesn't think it matters if he's a famous poet. Everyone dies in the end and everyone gets forgotten no matter how much of a big deal they were in their lives. Um, yay?