One of the biggest challenges for me was an infamous affair that I couldn’t really ignore. If you haven’t yet gotten to this part in Jewel of Persia (trust me, you’ll know if you have!) Then stop reading. Seriously. I had little choice but to make this a major pivot point in the book.
See, here are the facts according to Herodotus. Xerxes returned to Sardis after his defeat. When there, he fell in love with his brother Masistes’ wife (she’s unnamed in Herodotus), who refuses him. Thinking to keep her close when they return to Persia (normally she would have returned to her home in Bactra), he cleverly arranged an engagement between his eldest son, Darius, and her daughter, Artaynte. The two marry as soon as they return to Susa, but rather than pursuing the mother, Xerxes then falls in love with the daughter.
Herodotus tells us he “had success” with her and “she pleased him so well” that he agreed to grant her a boon. She asked for a shawl Xerxes wore all the time, one that Amestris had made him. He urges her to take a city instead (seriously, LOL), but she refuses and insists on the shawl. She then parades around the court in it during his birthday celebration. Enraged, Amestris asks for a favor. (Now, if the king agrees to grant a favor during his birthday feast, he’s legally bound to deliver it). She asks for Artaynte’s mother to be handed over to her, convinced the mother was behind this scheme. She then has this woman brutally mutilated. I’m talking chopping off so many body parts that she’s still alive when carried home but dies within an hour of reaching it.
Xerxes realizes as soon as he hears Amestris’s request that the poor woman’s life is over (Amestris was well known for her bloodthirsty ways) and rushes to his brother to try to soften the blow. He orders Masistes to divorce his wife and instead marry Xerxes’ eldest daughter, Amytis. Masistes refuses, which so enrages Xerxes that he says, “Then you shall have neither.” Masistes runs home, his wife dies in his arms, and he immediately rushes out, intending to rally an army and revolt. He’s captured and killed.
Yikes! Right? I mean, this guy is supposed to be my hero, but here he is doing THIS. Argh! How in the world am I supposed to deal with this??
But I knew from the get-go I’d have to, so I was very careful to work the motivation in throughout. I deliberately crafted Artaynte to be a puppet of her mother (whom I named Parsisa), and established conflict between Parsisa and Amestris. I also assigned to Artaynte a good (from her point of view) reason to do something so stupid and dangerous, when she was married to the heir apparent–a side of the story Herodotus ignores entirely. In fact, the only time this eldest son of Xerxes is named is in this story, and only when Xerxes arranges the marriage. I figured he had to be way more present than that.
I decided that Herodotus didn’t know these people’s thoughts and hearts any better than I could (he was writing well after they were all dead), so I made up my mind that it was okay to ignore his motivation and substitute my own. I could put my own twists and spins on it and stick to the bare (awful) facts.
And as it happens, it’s the catalyst for bringing Esther to the palace, so . . . well, just know that wasn’t from my imagination, it was recorded fact! 
This also became my explanation for the history that takes place after my story ends. Eight years after the close of Esther, Xerxes is assassinated through a plot originating in the harem. His two eldest sons, including Darius, were killed with him, and Artaxerxes, only 17, became king. Why? Well, in my version of events, it’s related to the way family relations fell out after The Affair.