Iron Gold will be the first book in a new trilogy set in the same universe as the Red Rising trilogy.
In an interview on the Hallmark channel, Pierce Brown stated that the story will be set approximately 10 years after the events of Morning Star. 
In an interview with Entertainment Weekly, Pierce explains more of the plot of the book:
The new Solar Republic, led by Darrow and Mustang, has replaced the Society on Mars, Earth, and Luna, and is locked in an existential struggle with the remaining Golds of the Core. A decade-long peace still exists between the Republic and the Golds of the Rim worlds, but something stirs in the darkness out beyond the asteroid belt.Also stated is that there will be four points of view, including that of Darrow, with two completely new characters.
The old world is dead. But what will rise from its ashes?
Darrow was born a slave. He became a weapon.
He ended centuries of Gold rule, broke the chains of an empire, and now he’s the hero of a brave new republic. But at terrible cost.
At the edge of the solar system, the grandson of the emperor he murdered dreams of revenge.
In his hidden fortress in the oceans of Venus, the Ash Lord lies in wait, plotting to crush the newborn democracy.
And, at home, a young Red girl who’s lost everything to the Rising questions whether freedom was just another Gold lie.
In a fearsome new world where Obsidian pirates roam the Belt, famine and genocide ravage Mars, and crime lords terrorise Luna, it’s time for Darrow and a cast of new characters from across the solar system to face down the chaos that revolution has unleashed.
- ↑ https://www.youtube.com/watch?v=BPQDBnJnBzQ&feature=youtu.be
- ↑ http://www.ew.com/article/2016/12/15/pierce-brown-iron-gold-cover-plot-new-red-rising-trilogy
- ↑ http://www.usatoday.com/story/life/books/2016/02/17/exclusive-pierce-brown-morning-star-red-rising-usa-today-best-selling-books/80451454/
- ↑ https://www.facebook.com/PierceBrownAuthor/posts/980247885441791